unix cat multiple files - don't cause error if one doesn't exist?

Question

I'm trying to cat a bunch of files, some of which may not exist. Now that's ok if some of them don't exist, but I don't want cat to return an error in this case, if possible. Here's my call:

zcat *_max.rpt.gz *_min.rpt.gz | gzip > temp.rpt.gz

When this command is run, either a bunch of files matching *_max.rpt.gz will exist, or *_min.rpt.gz will exist. If the other doesn't exist, I don't care, I just want to concatenate what I can. But I'm getting an error message which stops the rest of my code from running.

Anything I can do? Thanks.

score 36 · Accepted Answer · answered Oct 10 '12 at 22:02

36

Just redirect the stderr to /dev/null:

cat file1 file2 .... 2>/dev/null

If one or more files don't exist, then cat will give an error which will go to /dev/null and you'll get the desired result.

answered Oct 10 '12 at 22:02

P.P

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my man... I knew people used /dev/null for something. EDIT - not sure where to put 2>/dev/null in my line of code - after the pipe or before? – JDS Oct 10 '12 at 22:08
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@YoungMoney Before the pipe: `zcat *_max.rpt.gz *_min.rpt.gz 2>/dev/null | gzip > temp.rpt.gz` – P.P Oct 10 '12 at 22:11
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`cat` will return a **non-zero exit code** if it can't find one of the input files. – rustyx Oct 16 '18 at 08:57

score 11 · Answer 2 · answered Sep 11 '20 at 17:10

11

[ -f file.txt ] && cat file.txt

answered Sep 11 '20 at 17:10

user3167916

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score 8 · Answer 3 · edited Mar 01 '19 at 00:19

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grep -hs ^ file1 file2 ....

Unlike cat has zero return code. Option -h disables file name print, option -s disables file error reporting, ^ matches all lines.

edited Mar 01 '19 at 00:19

wass rubleff

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answered Dec 17 '18 at 15:19

orgoj

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On bash 4.2 I get error code 2 for `grep -hs ^ missing_file` – Noam Manos Jul 08 '20 at 21:53

score 5 · Answer 4 · answered Aug 27 '20 at 09:55

5

You can append || True to your commands to silence the exit code.

answered Aug 27 '20 at 09:55

DustWolf

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score 1 · Answer 5 · answered Oct 10 '12 at 22:03

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zcat `ls *.rpt.gz | grep -E '_(max|min)\.rpt\.gz$'` | gzip > temp.rpt.gz

Bit of a hack, but then so is the shell :-P

answered Oct 10 '12 at 22:03

j_random_hacker

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unix cat multiple files - don't cause error if one doesn't exist?

5 Answers5