Shell subcommand output to parent command

Question

I have a one line command, lets say

grep needle haystack.file

What if i wanted to replace "needle" with the current working directory using the pwd command. Now it might be possible using pipes but I need the needle part to show the working directory and the rest of the command to be the same.

So preferably something like this:

grep (pwd) haystack.file

Which when executed would actually run the following command:

grep /var/www/html/ haystack.file

I've done a bit of searching and have found a lot of examples with pipes but it cant be applied in my scenario as the first part (grep) and second part (haystack.file) is fixed in an application.

fedorqui · Accepted Answer · 2014-12-12 14:48:52Z

5

Use the $PWD variable, always set:

grep "$PWD" haystack.file

You can also use command substitution:

grep "$(pwd)" haystack.file

Note the importance of quotes. Do it! Otherwise strange things can happen.

answered Dec 12, 2014 at 14:48

fedorqui

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3 Comments

Marc B Over a year ago

grep `pwd` haystack.file would work as well, as long as there's no IFS chars in the path.

fedorqui Over a year ago

Yes! Only that I tend not to use ``: they cannot be nested :(

Etan Reisner Over a year ago

@MarcB It does but there is literally no reason to use `pwd` over "$(pwd)" and many reasons not to.

nu11p01n73R · Accepted Answer · 2014-12-12 14:56:22Z

5

You can use command substitution

Test

$ echo $(pwd) > test
$ grep $(pwd) test
/home/xxx/yyy

OR

$ grep `pwd` test
/home/xxx/yyy

Security

It's always recomended to quote the command substituion to take care of the spaces in the output of pwd command

Test

$ pwd
/home/xxx/yyy/hello world
$(pwd) > test

$ grep $(pwd) test #without quoting
grep: world: No such file or directory
test:/home/xxx/yyy/hello world

$ grep "$(pwd)" test #with quoting
/home/xxx/yyy/hello world

edited Dec 12, 2014 at 14:56

answered Dec 12, 2014 at 14:49

nu11p01n73R

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