Bash: How to remove the last character of a string?


 
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# 8  
Old 02-18-2012
Code:
echo $x | sed s/.$//

This User Gave Thanks to balajesuri For This Post:
# 9  
Old 02-18-2012
good shot bala .. Smilie
# 10  
Old 02-18-2012
Quote:
Originally Posted by balajesuri
Code:
echo $x | sed s/.$//

Yes, this works, but it is horribly inefficient. Consider these two scripts which both chop the last character from the string stored in 'foo' and assign it to 'x':

Code:
#!/usr/bin/env bash
foo="hello world"
for (( i = 0; i < 1000; i++ ))
do
    x="${foo%?}"
done

and

Code:
#!/usr/bin/env bash
foo="hello world"
for (( i = 0; i < 1000; i++ ))
do
    x=$(echo $foo | sed s/.$// )
done

The first, using shell string manipulation, takes about 2/100ths of a second to execute:

Code:
time script1

real    0m0.02s
user    0m0.01s
sys     0m0.01s

while the second script takes more than 5 seconds:

Code:
time script2

real    0m5.03s
user    0m1.05s
sys     0m3.80s

If I've done my math correctly, that's about 2500 times slower, just to do this one assignment. Imagine if the script needed to chop 100 strings in its loop and did them all this way?

You'll note that the majority of the time in the second script is system time -- that's the time that bash had to wait on the system to start each sed process and deal with the I/O from sed back to bash.

Last edited by agama; 02-18-2012 at 09:46 AM.. Reason: clarification in text
# 11  
Old 02-18-2012
Quote:
Originally Posted by agama
No math needed:

Code:
foo="hello world"
echo ${foo%?}
hello worl

Quote:
Originally Posted by codemaniac
We can achieve that easily with traditional POSIX filters .
Code:
echo $foo | cut -c 1-$(expr `echo "$foo" | wc -c` - 2)

Quote:
Originally Posted by balajesuri
Code:
echo $x | sed s/.$//

In my opinion, agama's solution is the best of the bunch. It doesn't require any external tools and uses only a standard sh parameter expansion operation.

However, the use of echo in each solution makes is unsuitable for general purpose usage. If, $foo or ${foo%?} were to expand to something beginning with a leading dash, something resembling an option, the pipeline could give an unexpected result.

I suggest using printf %s "${foo%?}" in lieu of echo.

Regards,
Alister
This User Gave Thanks to alister For This Post:
# 12  
Old 02-18-2012
I've tried to delete but for whatever reason I am not able to. I didn't want to post this here but I can not even send a pm about this... kind of annoying...

m
# 13  
Old 02-18-2012
Completely agree with you alister .
Thank you Agama for the enlightenment on the issue . Smilie
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