line of code

indiancosmonaut · 08-22-2007, 06:10 AM

I found this piece of code...
kindly help me in what the code does...?

Code:

echo "Usage: ${0##*/}"

Code:

$ ksh script.sh /home/user/somefile.txt
Usage: somefile.txt

Kindly advice,

indiancosmonaut

theYinYeti · 08-22-2007, 06:40 AM

I don't use ksh, but with bash at least ${variable##pattern} means:
- Display $variable where the longest match of pattern at the start of the initial value is removed.

Likewise, ${variable#pattern}, ${variable%%pattern} and ${variable%pattern} respectively mean:
- Display $variable where the shortest match of pattern at the start of the initial value is removed.
- Display $variable where the longest match of pattern at the end of the initial value is removed.
- Display $variable where the shortest match of pattern at the end of the initial value is removed.

There are other such usefull notations. See the man page.

Yves.

jlliagre · 08-22-2007, 03:08 PM

Quote:

Originally Posted by theYinYeti

I don't use ksh, but with bash at least ...

Same with ksh.
Actually this syntax was created in the Korn shell and later included in POSIX compliant shells including bash.

indiancosmonaut · 08-24-2007, 01:18 AM

Hi theYinYeti & jlliagre,

Thanks to both for the information.
Could you tell me which man page to refer.
Is it the ksh man page? I see it but there is no information regarding the constructs.

Kind regards,

indiancosmonaut

jlliagre · 08-24-2007, 01:51 AM

From the ksh manual page:

Code:

${parameter##word}       Remove Largest Prefix Pattern. The  word
                         is  expanded  to  produce a pattern. The
                         parameter  expansion  then  results   in
                         parameter,  with  the largest portion of
                         the  prefix  matched  by   the   pattern
                         deleted.

indiancosmonaut · 08-29-2007, 04:25 AM

Thanks jlliagre,

I was referring to some abridged doc.
Found the complete ksh man page!

I was referring and i found the following points.

1. ; causes sequential execution of the previous pipeline.
2. & causes asynchronous execution of the previous pipeline.
3. |& causes asynchronous execution of the previous pipeline with a two-way pipe established to the parent shell.

Could you help me out with some example for point 3.

Also,
What is the difference between

Code:

Command /dev/null 2>&1

and

Code:

Command 2>&1 /dev/null

Thanks in advance,

Kind regards,

indiancosmonaut