Related
This is a follow-up to my question here: How to write bash function to print and run command when the command has arguments with spaces or things to be expanded
Suppose I have this function to print and run a command stored in an array:
# Print and run the cmd stored in the passed-in array
print_and_run() {
echo "Running cmd: $*"
# run the command by calling all elements of the command array at once
"$#"
}
This works fine:
cmd_array=(ls -a /)
print_and_run "${cmd_array[#]}"
But this does NOT work:
cmd_array=(ls -a / | grep "home")
print_and_run "${cmd_array[#]}"
Error: syntax error near unexpected token `|':
eRCaGuy_hello_world/bash$ ./print_and_run.sh
./print_and_run.sh: line 55: syntax error near unexpected token `|'
./print_and_run.sh: line 55: `cmd_array=(ls -a / | grep "home")'
How can I get this concept to work with the pipe operator (|) in the command?
If you want to treat an array element containing only | as an instruction to generate a pipeline, you can do that. I don't recommend it -- it means you have security risk if you don't verify that variables into your string can't consist only of a single pipe character -- but it's possible.
Below, we create a random single-use "$pipe" sigil to make that attack harder. If you're unwilling to do that, change [[ $arg = "$pipe" ]] to [[ $arg = "|" ]].
# generate something random to make an attacker's job harder
pipe=$(uuidgen)
# use that randomly-generated sigil in place of | in our array
cmd_array=(
ls -a /
"$pipe" grep "home"
)
exec_array_pipe() {
local arg cmd_q
local -a cmd=( )
while (( $# )); do
arg=$1; shift
if [[ $arg = "$pipe" ]]; then
# log an eval-safe copy of what we're about to run
printf -v cmd_q '%q ' "${cmd[#]}"
echo "Starting pipeline component: $cmd_q" >&2
# Recurse into a new copy of ourselves as a child process
"${cmd[#]}" | exec_array_pipe "$#"
return
fi
cmd+=( "$arg" )
done
printf -v cmd_q '%q ' "${cmd[#]}"
echo "Starting pipeline component: $cmd_q" >&2
"${cmd[#]}"
}
exec_array_pipe "${cmd_array[#]}"
See this running in an online sandbox at https://ideone.com/IWOTfO
Do this instead. It works.
print_and_run() {
echo "Running cmd: $1"
eval "$1"
}
Example usage:
cmd='ls -a / | grep -C 9999 --color=always "home"'
print_and_run "$cmd"
Output:
Running cmd: ls -a / | grep -C 9999 --color=always "home"
(rest of output here, with the word "home" highlighted in red)
The general direction is that you don't. You do not store the whole command line to be printed later, and this is not the direction you should take.
The "bad" solution is to use eval.
The "good" solution is to store the literal '|' character inside the array (or some better representation of it) and parse the array, extract the pipe parts and execute them. This is presented by Charles in the other amazing answer. It is just rewriting the parser that already exists in the shell. It requires significant work, and expanding it will require significant work.
The end result is, is that you are reimplementing parts of shell inside shell. Basically writing a shell interpreter in shell. At this point, you can just consider taking Bash sources and implementing a new shopt -o print_the_command_before_executing option in the sources, which might just be simpler.
However, I believe the end goal is to give users a way to see what is being executed. I would propose to approach it like .gitlab-ci.yml does with script: statements. If you want to invent your own language with "debug" support, do just that instead of half-measures. Consider the following YAML file:
- ls -a / | grep "home"
- echo other commands
- for i in "stuff"; do
echo "$i";
done
- |
for i in "stuff"; do
echo "$i"
done
Then the following "runner":
import yaml
import shlex
import os
import sys
script = []
input = yaml.safe_load(open(sys.argv[1], "r"))
for line in input:
script += [
"echo + " + shlex.quote(line).replace("\n", "<newline>"), # some unicode like  would look nice
line,
]
os.execvp("bash", ["bash", "-c", "\n".join(script)])
Executing the runner results in:
+ ls -a / | grep "home"
home
+ echo other commands
other commands
+ for i in "stuff"; do echo "$i"; done
stuff
+ for i in "stuff"; do<newline> echo "$i"<newline>done<newline>
stuff
This offers greater flexibility and is rather simple, supports any shell construct with ease. You can try gitlab-ci/cd on their repository and read the docs.
The YAML format is only an example of the input format. Using special comments like # --- cut --- between parts and extracting each part with the parser will allow running shellcheck over the script. Instead of generating a script with echo statements, you could run Bash interactively, print the part to be executed and then "feed" the part to be executed to interactive Bash. This will alow to preserve $?.
Either way - with a "good" solution, you end up with a custom parser.
Instead of passing an array, you can pass the whole function and use the output of declare -f with some custom parsing:
print_and_run() {
echo "+ $(
declare -f "$1" |
# Remove `f() {` and `}`. Remove indentation.
sed '1d;2d;$d;s/^ *//' |
# Replace newlines with <newline>.
sed -z 's/\n*$//;s/\n/<newline>/'
)"
"$#"
}
cmd() { ls -a / | grep "home"; }
print_and_run cmd
Results in:
+ ls --color -F -a / | grep "home"
home/
It will allow for supporting any shell construct and still allow you to check it with shellcheck and doesn't require that much work.
I found here, a code for Bash to be able to find a missing file, and this code works great because I wont be able to know the length of the sequenced files, so this is able to find the missing file without requiring me to input the last number in the sequence.
This is the code:
shopt -s extglob
shopt -s nullglob
arr=( +([0-9]).#(psd) )
for (( i=10#${arr[0]%.*}; i<=10#${arr[-1]%.*}; i++ )); do
printf -v f "%05d" $i;
[[ ! -f "$(echo "$f".*)" ]] && echo "$f is missing"
done
And it works in both terminal and iTerm.
BUT, when used in my Applescript it always reply with file 00000 is missing, when it is not:
set AEPname to "AO-M1P8"
set RENDERfolder to quoted form of POSIX path of "Volumes:RAID STORAGE:CACHES:RENDERS:AE"
set ISAEDONE to do shell script "cd /Volumes/RAID\\ STORAGE/CACHES/RENDERS/AE/AO-M1P8/
#!/bin/bash
shopt -s extglob
shopt -s nullglob
arr=( +([0-9]).#(psd) )
for (( i=10#${arr[0]%.*}; i<=10#${arr[-1]%.*}; i++ )); do
printf -v f \"%05d\" $i;
[[ ! -f \"$(echo \"$f\".*)\" ]] && echo \"$f is missing\"
done
"
display dialog ISAEDONE as text
(*
if ISAEDONE contains "is missing" then
display dialog "FILE IS MISSING"
else
display dialog "ALL FINE"
end if
*)
What I am doing wrong or is there an easier way to accomplish this?
Thanks in advance.
Screenshot
UPDATE
Seems like the way I was doing it, makes the shell unable to get the directory of the files, If I do manually input the directory, seems like it should work, but now I am getting a new kind of error:
sh: line 6: arr: bad array subscript
sh: line 6: arr: bad array subscript
Strange since I don't get this error when manually pasting the code into terminal.
I updated the code.
I want to pipe the output of a "template" file into MySQL, the file having variables like ${dbName} interspersed. What is the command line utility to replace these instances and dump the output to standard output?
The input file is considered to be safe, but faulty substitution definitions could exist. Performing the replacement should avoid performing unintended code execution.
Update
Here is a solution from yottatsa on a similar question that only does replacement for variables like $VAR or ${VAR}, and is a brief one-liner
i=32 word=foo envsubst < template.txt
Of course if i and word are in your environment, then it is just
envsubst < template.txt
On my Mac it looks like it was installed as part of gettext and from MacGPG2
Old Answer
Here is an improvement to the solution from mogsie on a similar question, my solution does not require you to escale double quotes, mogsie's does, but his is a one liner!
eval "cat <<EOF
$(<template.txt)
EOF
" 2> /dev/null
The power on these two solutions is that you only get a few types of shell expansions that don't occur normally $((...)), `...`, and $(...), though backslash is an escape character here, but you don't have to worry that the parsing has a bug, and it does multiple lines just fine.
Sed!
Given template.txt:
The number is ${i}
The word is ${word}
we just have to say:
sed -e "s/\${i}/1/" -e "s/\${word}/dog/" template.txt
Thanks to Jonathan Leffler for the tip to pass multiple -e arguments to the same sed invocation.
Use /bin/sh. Create a small shell script that sets the variables, and then parse the template using the shell itself. Like so (edit to handle newlines correctly):
File template.txt:
the number is ${i}
the word is ${word}
File script.sh:
#!/bin/sh
#Set variables
i=1
word="dog"
#Read in template one line at the time, and replace variables (more
#natural (and efficient) way, thanks to Jonathan Leffler).
while read line
do
eval echo "$line"
done < "./template.txt"
Output:
#sh script.sh
the number is 1
the word is dog
I was thinking about this again, given the recent interest, and I think that the tool that I was originally thinking of was m4, the macro processor for autotools. So instead of the variable I originally specified, you'd use:
$echo 'I am a DBNAME' | m4 -DDBNAME="database name"
Create rendertemplate.sh:
#!/usr/bin/env bash
eval "echo \"$(cat $1)\""
And template.tmpl:
Hello, ${WORLD}
Goodbye, ${CHEESE}
Render the template:
$ export WORLD=Foo
$ CHEESE=Bar ./rendertemplate.sh template.tmpl
Hello, Foo
Goodbye, Bar
template.txt
Variable 1 value: ${var1}
Variable 2 value: ${var2}
data.sh
#!/usr/bin/env bash
declare var1="value 1"
declare var2="value 2"
parser.sh
#!/usr/bin/env bash
# args
declare file_data=$1
declare file_input=$2
declare file_output=$3
source $file_data
eval "echo \"$(< $file_input)\"" > $file_output
./parser.sh data.sh template.txt parsed_file.txt
parsed_file.txt
Variable 1 value: value 1
Variable 2 value: value 2
Here's a robust Bash function that - despite using eval - should be safe to use.
All ${varName} variable references in the input text are expanded based on the calling shell's variables.
Nothing else is expanded: neither variable references whose names are not enclosed in {...} (such as $varName), nor command substitutions ($(...) and legacy syntax `...`), nor arithmetic substitutions ($((...)) and legacy syntax $[...]).
To treat a $ as a literal, \-escape it; e.g.:\${HOME}
Note that input is only accepted via stdin.
Example:
$ expandVarsStrict <<<'$HOME is "${HOME}"; `date` and \$(ls)' # only ${HOME} is expanded
$HOME is "/Users/jdoe"; `date` and $(ls)
Function source code:
expandVarsStrict(){
local line lineEscaped
while IFS= read -r line || [[ -n $line ]]; do # the `||` clause ensures that the last line is read even if it doesn't end with \n
# Escape ALL chars. that could trigger an expansion..
IFS= read -r -d '' lineEscaped < <(printf %s "$line" | tr '`([$' '\1\2\3\4')
# ... then selectively reenable ${ references
lineEscaped=${lineEscaped//$'\4'{/\${}
# Finally, escape embedded double quotes to preserve them.
lineEscaped=${lineEscaped//\"/\\\"}
eval "printf '%s\n' \"$lineEscaped\"" | tr '\1\2\3\4' '`([$'
done
}
The function assumes that no 0x1, 0x2, 0x3, and 0x4 control characters are present in the input, because those chars. are used internally - since the function processes text, that should be a safe assumption.
here's my solution with perl based on former answer, replaces environment variables:
perl -p -e 's/\$\{(\w+)\}/(exists $ENV{$1}?$ENV{$1}:"missing variable $1")/eg' < infile > outfile
I would suggest using something like Sigil:
https://github.com/gliderlabs/sigil
It is compiled to a single binary, so it's extremely easy to install on systems.
Then you can do a simple one-liner like the following:
cat my-file.conf.template | sigil -p $(env) > my-file.conf
This is much safer than eval and easier then using regex or sed
Here is a way to get the shell to do the substitution for you, as if the contents of the file were instead typed between double quotes.
Using the example of template.txt with contents:
The number is ${i}
The word is ${word}
The following line will cause the shell to interpolate the contents of template.txt and write the result to standard out.
i='1' word='dog' sh -c 'echo "'"$(cat template.txt)"'"'
Explanation:
i and word are passed as environment variables scopped to the execution of sh.
sh executes the contents of the string it is passed.
Strings written next to one another become one string, that string is:
'echo "' + "$(cat template.txt)" + '"'
Since the substitution is between ", "$(cat template.txt)" becomes the output of cat template.txt.
So the command executed by sh -c becomes:
echo "The number is ${i}\nThe word is ${word}",
where i and word are the specified environment variables.
If you are open to using Perl, that would be my suggestion. Although there are probably some sed and/or AWK experts that probably know how to do this much easier. If you have a more complex mapping with more than just dbName for your replacements you could extend this pretty easily, but you might just as well put it into a standard Perl script at that point.
perl -p -e 's/\$\{dbName\}/testdb/s' yourfile | mysql
A short Perl script to do something slightly more complicated (handle multiple keys):
#!/usr/bin/env perl
my %replace = ( 'dbName' => 'testdb', 'somethingElse' => 'fooBar' );
undef $/;
my $buf = <STDIN>;
$buf =~ s/\$\{$_\}/$replace{$_}/g for keys %replace;
print $buf;
If you name the above script as replace-script, it could then be used as follows:
replace-script < yourfile | mysql
file.tpl:
The following bash function should only replace ${var1} syntax and ignore
other shell special chars such as `backticks` or $var2 or "double quotes".
If I have missed anything - let me know.
script.sh:
template(){
# usage: template file.tpl
while read -r line ; do
line=${line//\"/\\\"}
line=${line//\`/\\\`}
line=${line//\$/\\\$}
line=${line//\\\${/\${}
eval "echo \"$line\"";
done < ${1}
}
var1="*replaced*"
var2="*not replaced*"
template file.tpl > result.txt
I found this thread while wondering the same thing. It inspired me to this (careful with the backticks)
$ echo $MYTEST
pass!
$ cat FILE
hello $MYTEST world
$ eval echo `cat FILE`
hello pass! world
Lots of choices here, but figured I'd toss mine on the heap. It is perl based, only targets variables of the form ${...}, takes the file to process as an argument and outputs the converted file on stdout:
use Env;
Env::import();
while(<>) { $_ =~ s/(\${\w+})/$1/eeg; $text .= $_; }
print "$text";
Of course I'm not really a perl person, so there could easily be a fatal flaw (works for me though).
It can be done in bash itself if you have control of the configuration file format. You just need to source (".") the configuration file rather than subshell it. That ensures the variables are created in the context of the current shell (and continue to exist) rather than the subshell (where the variable disappear when the subshell exits).
$ cat config.data
export parm_jdbc=jdbc:db2://box7.co.uk:5000/INSTA
export parm_user=pax
export parm_pwd=never_you_mind
$ cat go.bash
. config.data
echo "JDBC string is " $parm_jdbc
echo "Username is " $parm_user
echo "Password is " $parm_pwd
$ bash go.bash
JDBC string is jdbc:db2://box7.co.uk:5000/INSTA
Username is pax
Password is never_you_mind
If your config file cannot be a shell script, you can just 'compile' it before executing thus (the compilation depends on your input format).
$ cat config.data
parm_jdbc=jdbc:db2://box7.co.uk:5000/INSTA # JDBC URL
parm_user=pax # user name
parm_pwd=never_you_mind # password
$ cat go.bash
cat config.data
| sed 's/#.*$//'
| sed 's/[ \t]*$//'
| sed 's/^[ \t]*//'
| grep -v '^$'
| sed 's/^/export '
>config.data-compiled
. config.data-compiled
echo "JDBC string is " $parm_jdbc
echo "Username is " $parm_user
echo "Password is " $parm_pwd
$ bash go.bash
JDBC string is jdbc:db2://box7.co.uk:5000/INSTA
Username is pax
Password is never_you_mind
In your specific case, you could use something like:
$ cat config.data
export p_p1=val1
export p_p2=val2
$ cat go.bash
. ./config.data
echo "select * from dbtable where p1 = '$p_p1' and p2 like '$p_p2%' order by p1"
$ bash go.bash
select * from dbtable where p1 = 'val1' and p2 like 'val2%' order by p1
Then pipe the output of go.bash into MySQL and voila, hopefully you won't destroy your database :-).
In place perl editing of potentially multiple files, with backups.
perl -e 's/\$\{([^}]+)\}/defined $ENV{$1} ? $ENV{$1} : ""/eg' \
-i.orig \
-p config/test/*
I created a shell templating script named shtpl. My shtpl uses a jinja-like syntax which, now that I use ansible a lot, I'm pretty familiar with:
$ cat /tmp/test
{{ aux=4 }}
{{ myarray=( a b c d ) }}
{{ A_RANDOM=$RANDOM }}
$A_RANDOM
{% if $(( $A_RANDOM%2 )) == 0 %}
$A_RANDOM is even
{% else %}
$A_RANDOM is odd
{% endif %}
{% if $(( $A_RANDOM%2 )) == 0 %}
{% for n in 1 2 3 $aux %}
\$myarray[$((n-1))]: ${myarray[$((n-1))]}
/etc/passwd field #$n: $(grep $USER /etc/passwd | cut -d: -f$n)
{% endfor %}
{% else %}
{% for n in {1..4} %}
\$myarray[$((n-1))]: ${myarray[$((n-1))]}
/etc/group field #$n: $(grep ^$USER /etc/group | cut -d: -f$n)
{% endfor %}
{% endif %}
$ ./shtpl < /tmp/test
6535
6535 is odd
$myarray[0]: a
/etc/group field #1: myusername
$myarray[1]: b
/etc/group field #2: x
$myarray[2]: c
/etc/group field #3: 1001
$myarray[3]: d
/etc/group field #4:
More info on my github
To me this is the easiest and most powerful solution, you can even include other templates using the same command eval echo "$(<template.txt):
Example with nested template
create the template files, the variables are in regular bash syntax ${VARIABLE_NAME} or $VARIABLE_NAME
you have to escape special characters with \ in your templates otherwhise they will be interpreted by eval.
template.txt
Hello ${name}!
eval echo $(<nested-template.txt)
nested-template.txt
Nice to have you here ${name} :\)
create source file
template.source
declare name=royman
parse the template
source template.source && eval echo "$(<template.txt)"
the output
Hello royman!
Nice to have you here royman :)
envsubst
please don't use anything else (ie. don't eval)
I am trying to save the result from find as arrays.
Here is my code:
#!/bin/bash
echo "input : "
read input
echo "searching file with this pattern '${input}' under present directory"
array=`find . -name ${input}`
len=${#array[*]}
echo "found : ${len}"
i=0
while [ $i -lt $len ]
do
echo ${array[$i]}
let i++
done
I get 2 .txt files under current directory.
So I expect '2' as result of ${len}. However, it prints 1.
The reason is that it takes all result of find as one elements.
How can I fix this?
P.S
I found several solutions on StackOverFlow about a similar problem. However, they are a little bit different so I can't apply in my case. I need to store the results in a variable before the loop. Thanks again.
Update 2020 for Linux Users:
If you have an up-to-date version of bash (4.4-alpha or better), as you probably do if you are on Linux, then you should be using Benjamin W.'s answer.
If you are on Mac OS, which —last I checked— still used bash 3.2, or are otherwise using an older bash, then continue on to the next section.
Answer for bash 4.3 or earlier
Here is one solution for getting the output of find into a bash array:
array=()
while IFS= read -r -d $'\0'; do
array+=("$REPLY")
done < <(find . -name "${input}" -print0)
This is tricky because, in general, file names can have spaces, new lines, and other script-hostile characters. The only way to use find and have the file names safely separated from each other is to use -print0 which prints the file names separated with a null character. This would not be much of an inconvenience if bash's readarray/mapfile functions supported null-separated strings but they don't. Bash's read does and that leads us to the loop above.
[This answer was originally written in 2014. If you have a recent version of bash, please see the update below.]
How it works
The first line creates an empty array: array=()
Every time that the read statement is executed, a null-separated file name is read from standard input. The -r option tells read to leave backslash characters alone. The -d $'\0' tells read that the input will be null-separated. Since we omit the name to read, the shell puts the input into the default name: REPLY.
The array+=("$REPLY") statement appends the new file name to the array array.
The final line combines redirection and command substitution to provide the output of find to the standard input of the while loop.
Why use process substitution?
If we didn't use process substitution, the loop could be written as:
array=()
find . -name "${input}" -print0 >tmpfile
while IFS= read -r -d $'\0'; do
array+=("$REPLY")
done <tmpfile
rm -f tmpfile
In the above the output of find is stored in a temporary file and that file is used as standard input to the while loop. The idea of process substitution is to make such temporary files unnecessary. So, instead of having the while loop get its stdin from tmpfile, we can have it get its stdin from <(find . -name ${input} -print0).
Process substitution is widely useful. In many places where a command wants to read from a file, you can specify process substitution, <(...), instead of a file name. There is an analogous form, >(...), that can be used in place of a file name where the command wants to write to the file.
Like arrays, process substitution is a feature of bash and other advanced shells. It is not part of the POSIX standard.
Alternative: lastpipe
If desired, lastpipe can be used instead of process substitution (hat tip: Caesar):
set +m
shopt -s lastpipe
array=()
find . -name "${input}" -print0 | while IFS= read -r -d $'\0'; do array+=("$REPLY"); done; declare -p array
shopt -s lastpipe tells bash to run the last command in the pipeline in the current shell (not the background). This way, the array remains in existence after the pipeline completes. Because lastpipe only takes effect if job control is turned off, we run set +m. (In a script, as opposed to the command line, job control is off by default.)
Additional notes
The following command creates a shell variable, not a shell array:
array=`find . -name "${input}"`
If you wanted to create an array, you would need to put parens around the output of find. So, naively, one could:
array=(`find . -name "${input}"`) # don't do this
The problem is that the shell performs word splitting on the results of find so that the elements of the array are not guaranteed to be what you want.
Update 2019
Starting with version 4.4-alpha, bash now supports a -d option so that the above loop is no longer necessary. Instead, one can use:
mapfile -d $'\0' array < <(find . -name "${input}" -print0)
For more information on this, please see (and upvote) Benjamin W.'s answer.
Bash 4.4 introduced a -d option to readarray/mapfile, so this can now be solved with
readarray -d '' array < <(find . -name "$input" -print0)
for a method that works with arbitrary filenames including blanks, newlines, and globbing characters. This requires that your find supports -print0, as for example GNU find does.
From the manual (omitting other options):
mapfile [-d delim] [array]
-d
The first character of delim is used to terminate each input line, rather than newline. If delim is the empty string, mapfile will terminate a line when it reads a NUL character.
And readarray is just a synonym of mapfile.
The following appears to work for both Bash and Z Shell on macOS.
#! /bin/sh
IFS=$'\n'
paths=($(find . -name "foo"))
unset IFS
printf "%s\n" "${paths[#]}"
If you are using bash 4 or later, you can replace your use of find with
shopt -s globstar nullglob
array=( **/*"$input"* )
The ** pattern enabled by globstar matches 0 or more directories, allowing the pattern to match to an arbitrary depth in the current directory. Without the nullglob option, the pattern (after parameter expansion) is treated literally, so with no matches you would have an array with a single string rather than an empty array.
Add the dotglob option to the first line as well if you want to traverse hidden directories (like .ssh) and match hidden files (like .bashrc) as well.
you can try something like
array=(`find . -type f | sort -r | head -2`) , and in order to print the array values , you can try something like echo "${array[*]}"
None of these solutions suited me because I didn't feel like learning readarray and mapfile. Here is what I came up with.
#!/bin/bash
echo "input : "
read input
echo "searching file with this pattern '${input}' under present directory"
# The only change is here. Append to array for each non-empty line.
array=()
while read line; do
[[ ! -z "$line" ]] && array+=("$line")
done; <<< $(find . -name ${input} -print)
len=${#array[#]}
echo "found : ${len}"
i=0
while [ $i -lt $len ]
do
echo ${array[$i]}
let i++
done
You could do like this:
#!/bin/bash
echo "input : "
read input
echo "searching file with this pattern '${input}' under present directory"
array=(`find . -name '*'${input}'*'`)
for i in "${array[#]}"
do :
echo $i
done
In bash, $(<any_shell_cmd>) helps to run a command and capture the output. Passing this to IFS with \n as delimiter helps to convert that to an array.
IFS='\n' read -r -a txt_files <<< $(find /path/to/dir -name "*.txt")
I'm trying to declare an empty array in Shell Script but I'm experiencing an error.
#!/bin/bash
list=$#
newlist=()
for l in $list; do
newlist+=($l)
done
echo "new"
echo $newlist
When I execute it, I get test.sh: 5: test.sh: Syntax error: "(" unexpected
Run it with bash:
bash test.sh
And seeing the error, it seems you're actually running it with dash:
> dash test.sh
test.sh: 5: test.sh: Syntax error: "(" unexpected
Only this time you probably used the link to it (/bin/sh -> /bin/dash).
I find following syntax more readable.
declare -a <name of array>
For more details see Bash Guide for Beginners: 10.2. Array variables.
In BASH 4+ you can use the following for declaring an empty Array:
declare -a ARRAY_NAME=()
You can then append new items NEW_ITEM1 & NEW_ITEM2 by:
ARRAY_NAME+=(NEW_ITEM1)
ARRAY_NAME+=(NEW_ITEM2)
Please note that parentheses () is required while adding the new items. This is required so that new items are appended as an Array element. If you did miss the (), NEW_ITEM2 will become a String append to first Array Element ARRAY_NAME[0].
Above example will result into:
echo ${ARRAY_NAME[#]}
NEW_ITEM1 NEW_ITEM2
echo ${ARRAY_NAME[0]}
NEW_ITEM1
echo ${ARRAY_NAME[1]}
NEW_ITEM2
Next, if you performed (note the missing parenthesis):
ARRAY_NAME+=NEW_ITEM3
This will result into:
echo ${ARRAY_NAME[#]}
NEW_ITEM1NEW_ITEM3 NEW_ITEM2
echo ${ARRAY_NAME[0]}
NEW_ITEM1NEW_ITEM3
echo ${ARRAY_NAME[1]}
NEW_ITEM2
Thanks to #LenW for correcting me on append operation.
Try this to see if you are oriented to dash or bash
ls -al /bin/sh
If it says /bin/sh -> /bin/dash, then type this:
sudo rm /bin/sh
sudo ln -s /bin/bash /bin/sh
Then type again:
ls -al /bin/sh*
then must says something like this:
/bin/sh -> /bin/bash
It means that now sh is properly oriented to Bash and your arrays will work.
DOMAINS=(1); if [[ ${DOMAINS-} ]]; then # true
unset DOMAINS; if [[ ${DOMAINS-} ]]; then # false
If the array is empty just do this:
NEWLIST=
You can check it with:
if [ $NEWLIST ] ; then
# do something
fi
a non empty array declaration looks like this:
NEWLIST=('1' '2' '3')
To fill an array during process:
ARRAY=("$(find . -name '*.mp3')")
Hope this helps