replacing .c by .o

nesta · 02-10-2007, 11:49 AM

hi all,

i have a variable var where

Code:

 var=mycfile.c

and i want to change it to be

Code:

mycfile.o

i tried the following command:

Code:

echo $var | sed 's/.c/.o/'

but i got the following result:

Code:

m.ofile.o

i.e whenever it finds c letter it works and absolutely it overrides the character before the c character or the character after it

jlliagre · 02-10-2007, 11:53 AM

Try:

Code:

sed 's/\.c/.o/'

"." means any character in regular expressions, so you need to escape it.

colucix · 02-10-2007, 12:18 PM

Another solution could be

Code:

echo $var | sed 's/c$/o/'

The $ sign match only the character at the end of the string.

osor · 02-10-2007, 12:20 PM

Quote:

Originally Posted by jlliagre

Try:

Code:

sed 's/\.c/.o/'

Or even better,

Code:

sed 's/\.c$/.o/'

Where the dollar sign indicates the end-of-line (in case your filename is something like “mycfile.is.cool.c”).

jr1 · 02-11-2007, 06:33 PM

If you're using bash, this can easily be accomplished without sed.

Code:

echo "${var/%.c/.o}"

You can check this page of the bash reference manual if that doesn't make sense to you.

(Edit: This post originally had "${var/%.c$/.o}" instead of "${var/%.c/.o}").

matthewg42 · 02-11-2007, 07:10 PM

..or also using bash like this (the ${var%pattern} expression returns the value of var with the shortest suffix matching pattern removed):

Code:

cfile=myfile.c
ofile=${cfile%.c}.o

If you're tying to write a script to build a program, you'd be better off using make. That's what it's for.

jr1 · 02-11-2007, 07:32 PM

Quote:

Originally Posted by matthewg42

..or also using bash like this (the ${var%pattern} expression returns the value of var with the shortest suffix matching pattern removed):

Code:

cfile=myfile.c
ofile=${cfile%.c}.o

The only problem with that is that it will append ".o" to strings that don't end ".c". My earlier example won't alter strings unless they end in ".c".

matthewg42 · 02-11-2007, 08:05 PM

Quote:

Originally Posted by jr1

The only problem with that is that it will append ".o" to strings that don't end ".c". My earlier example won't alter strings unless they end in ".c".

Ah yes, very true - could be important or irrelevant depending on how he's getting the original value.

unSpawn · 02-11-2007, 08:52 PM

Code:

# That doesn't work for me in Bash2? ;-p
var=mycfile.c
echo "${var/%.c$/.o}"
mycfile.c

# This does
echo "${var/%.c/.o}"
mycfile.o

jr1 · 02-12-2007, 01:10 AM

Quote:

Originally Posted by unSpawn

Code:

# That doesn't work for me in Bash2? ;-p
var=mycfile.c
echo "${var/%.c$/.o}"
mycfile.c

# This does
echo "${var/%.c/.o}"
mycfile.o

Doh. I must've had sed on my mind. The $ was a typo and, of course, it has no special meaning in bash's shell parameter expansion (it was looking for ".c$" at the end of the string).

I'll correct the original post.