Multiple pipes in shell implementation in C [duplicate] - c

This question already has answers here:
Connecting n commands with pipes in a shell?
(2 answers)
Closed 9 years ago.
I'm trying to implement a shell, and i got everything working perfectly fine, with the exception of multiple pipes.
i.e ls -l -a -F | tr [a-z] [A-Z] | sort how can i approach this? i know i have to create multiple pipes to solve this but how exactly to do it?
Can someone guide me in the right direction?
I currently manage only one pipe, but i'm not too sure on how to approach this when i have more than two pipes.
I was wondering if anyone could provide me with some pseudo-code n how to approach this problem


Just parse the string in order, when you get to a pipe symbol you fork off the last command and store the std in and std out. If you had a prior command you pump that commands std out to the std in of the new command. Then you loop.
Additional note:
The only difference between
A) thing1 > thing2
and
B) thing1 | thing2
Is this, in A) you are running thing1 (with fork) and setting the output to a file called thing2
In B) you are running both thing1 and thing2 with fork and setting the output of thing1 to the input of thing2.
So,
C) thing1 | thing2 | thing3
Is just the same, you need to run (fork) thing1, thing2, thing3 and set the output of thing1 to the intput of thing2, the output of thing2 to the input of thing3.
Pipe works just like > but you run the "target" with fork.


If you've indeed got everything working but multiple pipes, you can reduce them to single pipes using grouping or subshells.
{ ls -l -a -F | tr a-z A-Z; } | sort
(ls -l -a -F | tr a-z A-Z) | sort

Related

implementing I/O file(s) redirections + pipes

I'm writing a shell for school assignment !
I have figured it out how to implement redirections like that.
ls | cat | wc
My question is how can i combine piping + files redirection like :
ls | cat < input1 < input2 > output | wc
The only way i see to make this working is to create sub processes whith intermediates pipes (tees). Am i right or there is an easier way ?
Thank you in advance and sorry for bad english !

Vlookup-like function using awk in ksh

Disclaimers:
1) English is my second language, so please forgive any gramatical horrors you may find. I am pretty confident you will be able to understand what I need despite these.
2) I have found several examples in this site that address questions/problems similar to mine, though I was unfortunately not able to figure out the modifications that would need to be introduced to fit my needs.
3) You will find some text in capital letters here and there. Is is of course not me "shouting" at you, but only a way to make portions of text stand out. Plase do not consider this an act of unpoliteness.
4) For those of you who get to the bottom of this novella alive, THANKS IN ADVANCE for your patience, even if you do not get to be able to/feel like help/ing me. My disclamer here would be the fact that, after surfing the site for a while, I noticed that the most common "complaint" from people willing to help seems to be lack of information (and/or the lack of quality) provided by the ones seeking for help. I then preferred to be accused of overwording if need be... It would be, at least, not a common offense...
The "Problem":
I have 2 files (a and b for simplification). File a has 7 columns separated by commas. File b has 2 columns separated by commas.
What I need: Whenever the data in the 7th column of file a matches -EXACT MATCHES ONLY- the data on the 1st column of file b, a new line, containing the whole line of file a plus column 2 of file b is to be appended into a new file "c".
--- MORE INFO IN THE NOTES AT THE BOTTOM ---
file a:
Server Name,File System,Path,File,Date,Type,ID
horror,/tmp,foldera/folder/b/folderc,binaryfile.bin,2014-01-21 22:21:59.000000,typet,aaaaaaaa
host1,/,somefolder,test1.txt,2016-08-18 00:00:20.000000,typez,11111111
host20,/,somefolder/somesubfolder,usr.cfg,2015-12-288 05:00:20.000000,typen,22222222
hoster,/lol,foolie,anotherfile.sad,2014-01-21 22:21:59.000000,typelol,66666666
hostie,/,someotherfolder,somefile.txt,2016-06-17 18:43:12.000000,typea,33333333
hostile,/sad,folder22,higefile.hug,2016-06-17 18:43:12.000000,typeasd,77777777
hostin,/var,folder30,someotherfile.cfg,2014-01-21 22:21:59.000000,typo,44444444
hostn,/usr,foldie,tinyfile.lol,2016-08-18 00:00:20.000000,typewhatever,55555555
server10,/usr,foldern,tempfile.tmp,2016-06-17 18:43:12.000000,tipesad,99999999
file b:
ID,Size
11111111,215915
22222222,1716
33333333,212856
44444444,1729
55555555,215927
66666666,1728
88888888,1729
99999999,213876
bbbbbbbb,26669080
Expected file c:
Server Name,File System,Path,File,Date,Type,ID,Size
host1,/,somefolder,test1.txt,2016-08-18 00:00:20.000000,typez,11111111,215915
host20,/,somefolder/somesubfolder,usr.cfg,2015-12-288 05:00:20.000000,typen,22222222,1716
hoster,/lol,foolie,anotherfile.sad,2014-01-21 22:21:59.000000,typelol,66666666,1728
hostie,/,someotherfolder,somefile.txt,2016-06-17 18:43:12.000000,typea,33333333,212856
hostin,/var,folder30,someotherfile.cfg,2014-01-21 22:21:59.000000,typo,44444444,1729
hostn,/usr,foldie,tinyfile.lol,2016-08-18 00:00:20.000000,typewhatever,55555555,215927
server10,/usr,foldern,tempfile.tmp,2016-06-17 18:43:12.000000,tipesad,99999999,213876
Additional notes:
0) Notice how line with ID "aaaaaaaa" in file a does not make it into file c since ID "aaaaaaaa" is not present in file b. Likewise, line with ID "bbbbbbbb" in file b does not make it into file c since ID "bbbbbbbb" is not present in file a and it is therefore never looked out for in the first place.
1) Data is clearly completely made out due to confidenciality issues, though the examples provided fairly resemble what the real files look like.
2) I added headers just to provide a better idea of the nature of the data. The real files don't have it, so no need to skip them on the source file nor create it in the destination file.
3) Both files come sorted by default, meaning that IDs will be properly sorted in file b, while they will be most likely scrambled in file a. File c should preferably follow the order of file a (though I can manipulate later to fit my needs anyway, so no worries there, as long as the code does what I need and doesn't mess up with the data by combining the wrong lines).
4) VERY VERY VERY IMPORTANT:
4.a) I already have a "working" ksh code (attached below) that uses "cat", "grep", "while" and "if" to do the job. It worked like a charm (well, acceptably) with 160K-lines sample files (it was able to output 60K lines -approx- an hour, which, in projection, would yield an acceptable "20 days" to produce 30 million lines [KEEP ON READING]), but somehow (I have plenty of processor and memory capacity) cat and/or grep seem to be struggling to process a real life 5Million-lines file (both file a and b can have up to 30 million lines each, so that's the maximum probable amount of lines in the resulting file, even assuming 100% lines in file a find it's match in file b) and the c file is now only being feed with a couple hundred lines every 24 hours.
4.b) I was told that awk, being stronger, should succeed where the more weaker commands I worked with seem to fail. I was also told that working with arrays might be the solution to my performance problem, since all data is uploded to memory at once and worked from there, instead of having to cat | grep file b as many times as there are lines in file a, as I am currently doing.
4.c) I am working on AIX, so I only have sh and ksh, no bash, therefore I cannot use the array tools provided by the latter, that's why I thought of AWK, that and the fact that I think AWK is probably "stronger", though I might be (probably?) wrong.
Now, I present to you the magnificent piece of ksh code (obvious sarcasm here, though I like the idea of you picturing for a brief moment in your mind the image of the monkey holding up and showing all other jungle-crawlers their future lion king) I have managed to develop (feel free to laugh as hard as you need while reading this code, I will not be able to hear you anyway, so no feelings harmed :P ):
cat "${file_a}" | while read -r line_file_a; do
server_name_file_a=`echo "${line_file_a}" | awk -F"," '{print $1}'`
filespace_name_file_a=`echo "${line_file_a}" | awk -F"," '{print $2}'`
folder_name_file_a=`echo "${line_file_a}" | awk -F"," '{print $3}'`
file_name_file_a=`echo "${line_file_a}" | awk -F"," '{print $4}'`
file_date_file_a=`echo "${line_file_a}" | awk -F"," '{print $5}'`
file_type_file_a=`echo "${line_file_a}" | awk -F"," '{print $6}'`
file_id_file_a=`echo "${line_file_a}" | awk -F"," '{print $7}'`
cat "${file_b}" | grep ${object_id_file_a} | while read -r line_file_b; do
file_id_file_b=`echo "${line_file_b}" | awk -F"," '{print $1}'`
file_size_file_b=`echo "${line_file_b}" | awk -F"," '{print $2}'`
if [ "${file_id_file_a}" = "${file_id_file_b}" ]; then
echo "${server_name_file_a},${filespace_name_file_a},${folder_name_file_a},${file_name_file_a},${file_date_file_a},${file_type_file_a},${file_id_file_a},${file_size_file_b}" >> ${file_c}.csv
fi
done
done
One last additional note, just in case you wonder:
The "if" section was not only built as a mean to articulate the output line, but it servers a double purpose, while safe-proofing any false positives that may derive from grep, IE 100 matching 1000 (Bear in mind that, as I mentioned earlier, I am working on AIX, so my grep does not have the -m switch the GNU one has, and I need matches to be exact/absolute).
You have reached the end. CONGRATULATIONS! You've been awarded the medal to patience.

$ cat stuff.awk
BEGIN { FS=OFS="," }
NR == FNR { a[$1] = $2; next }
$7 in a { print $0, a[$7] }
Note the order for providing the files to the awk command, b first, followed by a:
$ awk -f stuff.awk b.txt a.txt
host1,/,somefolder,test1.txt,2016-08-18 00:00:20.000000,typez,11111111,215915
host20,/,somefolder/somesubfolder,usr.cfg,2015-12-288 05:00:20.000000,typen,22222222,1716
hoster,/lol,foolie,anotherfile.sad,2014-01-21 22:21:59.000000,typelol,66666666,1728
hostie,/,someotherfolder,somefile.txt,2016-06-17 18:43:12.000000,typea,33333333,212856
hostin,/var,folder30,someotherfile.cfg,2014-01-21 22:21:59.000000,typo,44444444,1729
hostn,/usr,foldie,tinyfile.lol,2016-08-18 00:00:20.000000,typewhatever,55555555,215927
server10,/usr,foldern,tempfile.tmp,2016-06-17 18:43:12.000000,tipesad,99999999,213876

EDIT: Updated calculation
You can try to predict how often you are calling another program:
At least 7 awk's + 1 cat + 1 grep for each line in file a multiplied by 2 awk's for each line in file b.
(9 * 160.000).
For file b: 2 awk's, one file open and one file close for each hit. With 60K output, that would be 4 * 60.000.
A small change in the code can change this into "only" 160.000 times a grep:
cat "${file_a}" | while IFS=, read -r server_name_file_a \
filespace_name_file_a folder_name_file_a file_name_file_a \
file_date_file_a file_type_file_a file_id_file_a; do
grep "${object_id_file_a}" "${file_b}" | while IFS="," read -r line_file_b; do
if [ "${file_id_file_a}" = "${file_id_file_b}" ]; then
echo "${server_name_file_a},${filespace_name_file_a},${folder_name_file_a},${file_name_file_a},${file_date_file_a},${file_type_file_a},${file_id_file_a},${file_size_file_b}"
fi
done
done >> ${file_c}.csv
Well, try this with your 160K files and see how much faster it is.
Before I explain that this still is the wrong way I will make another small improvement: I will move the cat for the while loop to the end (after done).
while IFS=, read -r server_name_file_a \
filespace_name_file_a folder_name_file_a file_name_file_a \
file_date_file_a file_type_file_a file_id_file_a; do
grep "${object_id_file_a}" "${file_b}" | while IFS="," read -r line_file_b; do
if [ "${file_id_file_a}" = "${file_id_file_b}" ]; then
echo "${server_name_file_a},${filespace_name_file_a},${folder_name_file_a},${file_name_file_a},${file_date_file_a},${file_type_file_a},${file_id_file_a},${file_size_file_b}"
fi
done
done < "${file_a}" >> ${file_c}.csv
The main drawback of the solutions is that you are reading the complete file_b again and again with your grep for each line in file a.
This solution is a nice improvement in the performance, but still a lot overhead with grep. Another huge improvement can be found with awk.
The best solution is using awk as explained in What is "NR==FNR" in awk? and found in the answer of #jas.
It is only one system call and both files are only read once.

Bash executing a subset of lines in script

I have a file which contains commands similar to:
cat /home/ptay89/test/01.out
cat /home/ptay89/testing/02.out
...
But I only want a few of them executing. For example, if I only want to see the output files ending in 1.out, I can do this:
cat commands | grep 1.out | sh
However, I get the following output for each of the lines in the commands file:
: cannot be loaded - no such file or directoryst/01.out
When I copy and past the commands I want from the file directly, it works fine. Are there better ways of doing this?

You probably have spurious carriage returns in your file (created under Windows?). Use tr instead of cat to remove them:
tr -d '\015' <commands | grep 1.out | sh

Try doing a
grep -e '^cat.*out' commands | grep 1.out | sh
That should ignore any weird characters and take only the ones you need.

Multiple pipes in C

I want to implement multi pipes in c so I can do something like this, where ||| means duplicate the stdin to N pipe commands):
cat /tmp/test.log ||| wc -l ||| grep test1 ||| grep test2 | grep test3
This will return to me the number of lines in the file and the lines in the file that contain 'test1' string and the lines in the file that contain 'test2' && 'test3' string
In other words this would have the effect of these 3 regular pipelines:
cat /tmp/test.log | wc -l --> stdout
| grep test1 --> stdout
| grep test2 | grep test3 --> stdout
Has someone already implementated something like this? I didn't find anything...
NOTE: I know it can be done with scripting languages or with bash multiple file descriptors, but I am searching C code to do it.
Thanks!

Maybe your should start off with the tee command and examine their code.

Because it is impossible in C to have more than one process (or thread) read the same file descriptor without draining the data read, all solutions will have to store the data read in a temporary file and then each read the temp file.

How to make a pipe loop in Zsh?

Penz says that the problem could be solved by Multios and coproc features in the thread.
However, I am unsure about the solution.
I do know that you can use multios as
ls -1 > file | less
but I have never used such that you have two inputs.
How can you use these features to have a pipe loop in Zsh?

I am having trouble understanding the questions.
Are you trying to do the following:
(ls -1 && file) | less
Where && is used for multiple commands on a single line.
Or are you trying to do the following:
ls -1 | tee file | less
Where tee puts the output into the file and standard out.

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