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I have a file with list of directories:

$ cat dirs.txt
/some/path
/other/path
/some/another/one

Current directory is /home/loom

$ echo $PWD
/home/loom

I would like to add $PWD to each row of dirs.txt like the following: 

/home/loom/some/path
/home/loom/other/path
/home/loom/some/another/one

I unsuccessfully tried the command:

$ cat dirs.txt | awk '{print $PWD$1}'
/some/path/some/path
/other/path/other/path
/some/another/one/some/another/one

It just doubled each row. What command solves my problem?

I mean parametric answer, not cat dirs.txt | awk '{print "/home/loom" $1}'

jesse_b
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Loom
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2 Answers2

3

PWD is a shell variable and therefore won't expand inside the single quotes used by awk.

awk -v pwd="$PWD" '{print pwd$1}' dirs.txt

This will set the pwd awk variable to the value of the PWD shell variable and then print column 1 of each line in dirs.txt with that value prepended to the beginning.

Using GNU awk you can use the -i inplace option to overwrite your file with the output, otherwise you will have to redirect it to a new file and overwrite the old file with that if desired.

jesse_b
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  • +1. BTW, if the variable has been exported, you can use the awk built-in array `ENVIRON`. e.g. `awk '{print ENVIRON["PWD"]$1}' dirs.txt`. Using `-v` makes for more readable code, IMO. Also watch out for filenames containing the `=` character: awk will interpret them as variable assignments similar to `-v` (but this happens **after** any BEGIN block). e.g. `echo | awk '{print foo}' foo=bar` – cas Aug 16 '19 at 02:15
  • The functional difference between using `-v` and `ENVIRON` is that the former will expand escape sequences (so `foo\tbar` will become `foobar`) while the latter won't. You can use ENVIRON for non-exported variables too, you just need to set the shell variable to itself on the awk command line, e.g. `shellvar="$shellvar" awk 'BEGIN { awkvar=ENVIRON["shellvar"]...`. The issue about `=` (or `-`) in file names only applies to arguments, not to input. – Ed Morton Aug 16 '19 at 13:01
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There're of course more ways to do so, so since you're asking for any command that solves your problem, another way could be this:

while read -r line; do echo "${PWD}${line}"; done < "dirs"
pavelsaman
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    See [why-is-using-a-shell-loop-to-process-text-considered-bad-practice](https://unix.stackexchange.com/questions/169716/why-is-using-a-shell-loop-to-process-text-considered-bad-practice) – Ed Morton Aug 16 '19 at 12:57
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    Thank you, learnt a few things. – pavelsaman Aug 17 '19 at 07:53