How to use Unix to pass all lines as parameters to a script

Question

I have a file called pids.txt that contains lines, such as the following:

123
456
789

Then, I wrote a Python script that does something with each line. The Python script gets run like:

my_script.py 123 456 789 -a "something here" -b "something else"

I am stuck at the part where I want to run a Unix command, piping the outputs of pids.txt to my_script.py. I think you have to do something with cat?

(This doesn't work)

cat pids.txt | ./myscript.py -a "something here" -b "something else"

Any idea?

Adam Zalcman · Accepted Answer · 2011-11-17 14:01:25Z

5

You can use the $(command) construct (equivalent of backticks: `command`):

./myscript.py $(cat pids.txt) -a "something here" -b "something else"

The construct $(command) runs the command and substitutes the standard output of the command where the construct is placed.

Bash also provides you with $(< file) construct:

./myscript.py $(< pids.txt) -a "something here" -b "something else"

This reads the pids.txt file and substitutes its contents for the $(< ...) construct. (Thanks for this one go to glenn jackman)

edited Nov 17, 2011 at 14:01

answered Nov 16, 2011 at 23:55

Adam Zalcman

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2 Comments

glenn jackman Over a year ago

for bash, you can avoid calling out to cat with $(< pids.txt) that is run inside the shell.

glenn jackman Over a year ago

@Jeff, note the $(< pids.txt) portion is NOT quoted, so each line will be passed to your python program as a separate argument. If you were to write `"$(<pids.txt)" you would get a single, newline-separated, argument.

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