5 Jan
2023
5 Jan
'23
7:51 a.m.
On 1/4/23 02:29, Adam Thornton wrote:
> On Jan 3, 2023, at 10:26 AM, Dan Cross
<crossd(a)gmail.com> wrote:
>
>
> A few years ago, I was having lunch with some folks from the Go team
> and one of them remarked, "you shouldn't write a shell script that's
> longer than about 10 lines. Once you do, it's time to rewrite it in a
> real programming language." I was a bit taken aback, but they had a
> point. I'll note that Go standardized on using bash everywhere.
I have many counterexamples that take more than 10 lines. I'll show a couple
that are very useful to me:
# man_section() prints specific manual page sections (DESCRIPTION, SYNOPSIS,
# ...) of all manual pages in a directory (or in a single manual page file).
# Usage example: .../man-pages$ man_section man2 SYNOPSIS 'SEE ALSO';
man_section()
{
if [ $# -lt 2 ]; then
&2 echo "Usage: ${FUNCNAME[0]} <dir>
<section>...";
return $EX_USAGE;
fi
local page="$1";
shift;
local sect="$*";
find "$page" -type f \
|xargs wc -l \
|grep -v -e '\b1 ' -e '\btotal\b' \
|awk '{ print $2 }' \
|sort \
|while read -r manpage; do
(sed -n '/^\.TH/,/^\.SH/{/^\.SH/!p}' <"$manpage";
for s in $sect; do
<"$manpage" \
sed -n \
-e "/^\.SH $s/p" \
-e "/^\.SH $s/,/^\.SH/{/^\.SH/!p}";
done;) \
|man -P cat -l - 2>/dev/null;
done;
}
I don't think it's unreadable by being too long, and in every other language it
would take a lot more work to implement. And here's another one, which I used a
lot until I wrote grepc(1)[1]:
# grep_syscall() finds the prototype of a syscall in the kernel sources,
# printing the filename, line number, and the prototype.
# It should be run from the root of the linux kernel source tree.
# Usage example: .../linux$ grep_syscall openat2;
#
# See also: grepc(1)
grep_syscall()
{
if [ $# -ne 1 ]; then
&2 echo "Usage: ${FUNCNAME[0]}
<syscall>";
return $EX_USAGE;
fi
find ./* -type f \
|grep '\.c$' \
|xargs grep -l "$1" \
|sort \
|xargs pcregrep -Mn "(?s)^\w*SYSCALL_DEFINE.\($1\b.*?\)" \
|sed -E 's/^[^:]+:[0-9]+:/&\n/';
find ./* -type f \
|grep '\.[ch]$' \
|xargs grep -l "$1" \
|sort \
|xargs pcregrep -Mn "(?s)^asmlinkage\s+[\w\s]+\**sys_$1\s*\(.*?\)" \
|sed -E 's/^[^:]+:[0-9]+:/&\n/';
}
Cheers,
Alex
[1]: <http://www.alejandro-colomar.es/src/alx/alx/grepc.git/>
My number is larger than 10, but it's smaller than 100.