how to substr ?

black · 12-13-2002, 04:56 AM

Hi folks~

I touched shell programming not so long and now I need a way to get only part of a directory path. for example I have the folder as follows:
/black/goodie/games/warcraft
and what I expect is like this:
/black/goodie/games

and I knew in other programming languages there may be a function like substr could handle it and how about in shell(bash to me) ?

thanx in advance~

acid_kewpie · 12-13-2002, 05:13 AM

well we can't say how to get from a to be here as we really have no idea of the context. do you want to remove the last directory? do you want to remove the word "warcraft"? whatever it is that you want will no doubt be acoomplished using sed and/or tr and/or cut, but without a proper scenario it's not possible to actually tell you the answer. cehck the manpages though, super bed time reading!

black · 12-13-2002, 05:33 AM

oh I'll check sed and cut for more help~

I'd really appreciate your information, thanx acid_kewpie~

Hko · 12-16-2002, 10:46 AM

If you have the full path of a file in a shell variable, say "$SOMEFILE",
you can take substrings from the variable by using sed, cut, awk, etc.
If you only want to take directory or file names from a full path, it's probably easier to use the "basename" or the "dirname" utility. See their man pages.

But the bash shell, can do some simple substrings itself. This is easier to learn, and it's faster. Some examples:

Code:

# asuming warcraft is a file, so there'll be no trailing '/'
SOMEFILE=/black/goodie/games/warcraft

# strip directory:
FILENAME=${SOMEFILE##*/}
# This means: Remove longest possible part ('##') from the
# beginning of variable SOMEFILE that matches the wildcard
# pattern ('*/').
# So FILENAME becomes the $SOMEFILE with all characters
# removed up to (and including) the last slash.
echo $FILENAME

# strip filename:
DIRNAME=${SOMEFILE%/*}
# This means: Remove the shortest possible part ('%') from the
# end that matches '/*'.
echo $DIRNAME

# Take a substring using character positions (zero based)
# This example takes out "goodie" from the path, by 
# taking the substring of 6 characters, starting with character
# number 7:
TMP=${SOMEFILE:7:6}
echo $TMP

lackluster · 12-16-2002, 05:09 PM

thanks, Hko

that was really helpful.

tana · 12-23-2002, 12:39 AM

An excellant reference for such shell scripting can be found in Chapter 9.2 of the Advanced Bash - Scripting Guide at the Linux Documentation Project (http://www.tldp.org/guides.html).