Combining two cat statements into a single cat statement within bash

Question

I want to combine 2 different cat statements into a single cat statement

cat /dir1/file1.cfg | grep -q "linux"

cat /dir1/file2.cfg | grep -q "linux"

is there an OR operation that can be used here to do the grep -q "linux" on 2 files?

In this case, why not just use: `cat /dir1/file*.cfg | grep -q "linux"`? — Joaquin, Aug 08 '18 at 16:13
That is the original function of `cat`: To **conCATenate** and print files. In this case, you can use [brace expansion](https://www.gnu.org/software/bash/manual/html_node/Brace-Expansion.html#Brace-Expansion) and do `cat /dir1/file{1..2}.cfg | grep -q "linux"` — dawg, Aug 08 '18 at 16:53
As mentioned above -- if you *don't* want to concatenate multiple files, you **shouldn't be using `cat` at all**; it's much more efficient to give `grep` a direct handle on the files to search rather than forcing it to read from a FIFO connected to a separate process that is itself responsible for reading from the files. (With `grep`, actually, it may or may not be that significant -- but for `wc -c`, or `sort`, or `tail`, or other programs that can parallelize, seek, bisect, or otherwise use optimized implementations when given a real file handle the difference can be huge). — Charles Duffy, Aug 08 '18 at 16:54

score 2 · Accepted Answer · answered Aug 08 '18 at 16:13

2

What have you tried so far?

How about:

cat /dir1/file1.cfg /dir1/file2.cfg | grep -q "linux"

or with a subshell:

(cat /dir1/file1.cfg; cat /dir1/file2.cfg) | grep -q "linux"

or just:

grep -q "linux" /dir1/file1.cfg /dir1/file2.cfg

answered Aug 08 '18 at 16:13

domen

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cat is literally short for concatenate. you can just do `cat file1 file2 | grep ...` – jeremysprofile Aug 08 '18 at 16:25
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`{ cat ...; cat ...; }` would be slightly more efficient than `(cat ...; cat ...)`. – chepner Aug 08 '18 at 16:52

keithpjolley · Answer 2 · 2018-08-08T16:38:36.320

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These all give equivalent results. The last would be how I'd write it.

% (cat f1; cat f2) | grep -q "linux"
% (cat f1 f2) | grep -q "linux"
% grep -q "linux" f1 f2

edited Aug 08 '18 at 16:38

answered Aug 08 '18 at 16:14

keithpjolley

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score 0 · Answer 3 · answered Aug 09 '18 at 08:42

There's really no need for cat at all - grep will happily take its input from multiple files; normally, you need to tell it not to prefix the file name to the output lines, but since you're using -q, even that isn't necessary:

grep -q "linux" /dir1/file[12].cfg

(I've used a shell glob to save writing the repeated parts of the filename there).

Combining two cat statements into a single cat statement within bash

3 Answers3