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SoftTimur
SoftTimur

Reputation: 5490

Conditional check in a shell

I have a python script p.py which does exit("ABC") for some files. I would like to write a Ubuntu shell to copy the files which make the script exit("ABC") into a folder:

#!/bin/bash

FILES=*.txt
TOOL=p.py
TAREGT=../TARGET/

for f in $FILES
do
    if [ $(python $TOOL $f) = "ABC" ]
    then
        echo "$f"
        cp $f $TARGET
    fi
done

but the condition check if [ $(python $TOOL $f) = "ABC" ] does not seem to work, it says ./filter.sh: line 13: [: =: unary operator expected. Could anyone tell me what is wrong?

Upvotes: 0

Views: 239

Answers (1)

DevSolar
DevSolar

Reputation: 70213

The parameter to exit() is what the Python script returns (success / error). (Documentation of Python's exit(). Note how exit( "ABC" ) doesn't return "ABC", but prints that to stderr and returns 1.)

The return code is what ends up in the $? variable of the calling shell, or what you would test for like this:

# Successful if return code zero, failure otherwise.
# (This is somewhat bass-ackwards when compared to C/C++/Java "if".)
if python $TOOL $f
then
    ...
fi

The $(...) construct is replaced with the output of the called script / executable, which is a different thing altogether.

And if you're comparing strings, you have to quote them

if [ "$(python $TOOL $f)" = "ABC" ]

or use bash's improved test [[:

if [[ $(python $TOOL $f) = "ABC" ]]

Upvotes: 1

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