Comments on: Keeping You in the Loop – Bash For, While, Until Loop Examples

By: jalal hajigholamali

jalal hajigholamali — Mon, 11 Jul 2011 08:33:48 +0000

Hi,

great….

By: adyxax

adyxax — Fri, 09 Jul 2010 12:48:40 +0000

Yes, I will grant you that those are both external commands. I just can’t stand to see people using the awk and sed here and there because, as wonderfull and lovely those commands are, it’s quite overkill for so simple tasks.

Programming well in *sh is related to how many commands you know/understand, and using simple commands to do simple tasks is always good for your karma (and it’s more readable as far as bash is readable).

Otherwise yes, the efficient way to do this replacement is using bash internals, as you suggest.

By: Chris F.A. Johnson

Chris F.A. Johnson — Thu, 08 Jul 2010 17:03:54 +0000

Using basename is no better than awk. They are both external commands.
The shell can do it internally using parameter expansion:

filename=whatever.zip
name=${filename%.*}

By: adyxax

adyxax — Thu, 08 Jul 2010 14:56:17 +0000

I saw you are using awk to remove the .zip extension using awk in the first example :
# Skip the extension .zip
dirname=`echo ${file} | awk -F’.’ ‘{print $1}’`

I just wanted to suggest using the “basename” command for this kind of purposes : basename ${file} .zip

By: Chris F.A. Johnson

Chris F.A. Johnson — Tue, 06 Jul 2010 15:14:04 +0000

man bash:

Parameter Expansion
…
${parameter#word}
${parameter##word}
Remove matching prefix pattern. The word is expanded to produce
a pattern just as in pathname expansion. If the pattern matches
the beginning of the value of parameter, then the result of the
expansion is the expanded value of parameter with the shortest
matching pattern (the ”#” case) or the longest matching
pattern (the ”##” case) deleted. If parameter is @ or *, the
pattern removal operation is applied to each positional
parameter in turn, and the expansion is the resultant list. If
parameter is an array variable subscripted with @ or *, the
pattern removal operation is applied to each member of the array
in turn, and the expansion is the resultant list.

By: insomnia

insomnia — Tue, 06 Jul 2010 14:19:23 +0000

Thanks!Great job!
I have a question: what does “##” in “${file##/*/}” means?

By: Chris F.A. Johnson

Chris F.A. Johnson — Mon, 05 Jul 2010 21:33:57 +0000

fs, those are only the same if $file begins with a slash.

By: fs

fs — Mon, 05 Jul 2010 13:52:26 +0000

Nice tut! thanks!
but in Bash For … 1
shouldn’t
${file##*/}
be the same as
${file##/*/}
or I’m missing something?
By!

By: Chris F.A. Johnson

Chris F.A. Johnson — Mon, 28 Jun 2010 08:28:17 +0000

> exec while read line

That will not read the entire line if there is whitespace at the beginning or end of a line, and it will not read the line exactly as it is in the file if there are escaped characters in the line. The command should be:

while IFS= read -r line

> echo $line

That will not print the line exactly as it was in the file if there are consecutive whitespace characters in the line. Multiple whitespace characters will be replaced by a single space. It should be:

echo “$line”

And even that will not print the line correctly if $line contains, for example, “-n whatever”. When the contents of a variable are unknown, use printf:

printf “%s\n” “$line”