Bash script function return value problem

Question

Can anyone help me return the correct value from a bash script function?

Here's my function that should return first (and only) line of the file passed as an argument:

LOG_FILE_CREATION_TIME()
{
    return_value=`awk 'NR==1' $1`
    return return_value
}

And here's my call of that function in the other script:

LOG_FILE_CREATION_TIME "logfile"
timestamp=$?
echo "Timestamp = $timestamp"

I always get some random values with this code. If, for example, there's a value of 62772031 in the "logfile", I get

Timestamp = 255

as an output. For some other values in the file, I get other random values as a return value, never the correct one.

Any ideas?

Keith · Accepted Answer · 2010-12-27 11:02:29Z

7

Shell functions work like commands. They can only return errorlevel values (integers). To get strings you can either set a global variable, or print/echo the value and then have the caller use the command substitution (like back-ticks).

This works:

#!/bin/bash

LOG_FILE_CREATION_TIME()
{
    return_value=`awk 'NR==1' $1`
    echo $return_value
}

timestamp=$(LOG_FILE_CREATION_TIME $1)

echo $timestamp

Unrelated, but BTW in Python:

#!/usr/bin/python2

import sys
print open(sys.argv[1]).readline()

;-)

edited Dec 27, 2010 at 11:02

answered Dec 27, 2010 at 10:57

Keith

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2 Comments

plundra Over a year ago

Really, Python to perform head -1? There will be A LOT of answers if we were to implement it in all languages...

Keith Over a year ago

@plundra I'm assuming there will be more to this program than this. Sure, head -1 works best for a one-time thing. I was hinting that the OP might go down a different path than writing a large program with functions in shell.

plundra · Accepted Answer · 2010-12-27 10:57:47Z

5

The exit code is limited to 0 - 255, you cannot use it for a timestamp.

Echo your timestamp instead, since you don't seem to be outputing anything else; this ought to be fine?

LOG_FILE_CREATION_TIME()
{
    # If you want to do some more stuff, you might want
    # to use the intermediate variable as you first did.
    awk 'NR==1' $1
}

timestamp=$(LOG_FILE_CREATION_TIME "logfile")
echo "Timestamp = $timestamp"

You might have simplified the function in your example, because if all you wanted was the first line, why not use head -1 logfile instead?

answered Dec 27, 2010 at 10:57

plundra

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2 Comments

Eedoh Over a year ago

Do you know how could I do this in sh, instead of bash. In sh timestamp=$(LOG_FILE_CREATION_TIME "logfile") doesn't work. It says 'timestamp=$' unexpected

plundra Over a year ago

@Eedoh try using backticks, timestamp=`...`

agelbess · Accepted Answer · 2012-11-16 13:19:01Z

0

Another way is to use a global variable. You can have multiple "return" variables this way. It does not actually return anything, but does the trick.

#!/bin/sh
concat_ret
concat() {
 for s in $*
 do
 concat_ret="$concat_ret $s"
 done
 return 0
}
echo "starting"
concat String1 String2 String3 "and many other strings"
echo $?
echo $concat_ret
exit 0

Output

starting
0
String1 String2 String3 and many other strings

answered Nov 16, 2012 at 13:19

agelbess

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