Search for a pattern at the beginning of a line using grep

$ps -e "kworker$"
error: unknown sort specifier

Usage:
 ps [options]

 Try 'ps --help '
  or 'ps --help '
 for additional help text.

For more details see ps(1).
$ps -ef | grep "^daemon"
daemon     639     1  0 May04 ?        00:00:00 /usr/sbin/atd -f
$ps -ef | grep "^rtkit"
rtkit     1245     1  0 May04 ?        00:00:00 /usr/lib/rtkit/rtkit-daemon
$ps -ef | grep "^systemd+"
systemd+   522     1  0 May04 ?        00:00:00 /lib/systemd/systemd-timesyncd
$

Tinkering with trap and exit commands

TYPICAL COMMANDLINE SESSION
[bash]
$echo $?
0
$echo $?
0
$exit 10 | tee solve.txt
$cat solve.txt
$rm solve.txt
$exit 10 | echo $?
0
$exit -1 | echo $?
0
$exit -1 | echo $?
0
$false | true
$echo $?
0
$false
$echo $?
1
$true
$echo $?
0
$exit 5 | tee var=$?
$file var\=0
var=0: empty
$type var
bash: type: var: not found
$file var\=0
var=0: empty
$
[/bash]

[bash]
$trap $? > solve.txt exit 10
$cat solve.txt
Display all 296 possibilities? (y or n)
$cat solve.txt
$trap echo $? > solve.txt exit 10
$cat solve.txt
$trap `echo $? > solve.txt` exit 10
$cat solve.txt
0
$
[/bash]

[bash]
$bash -c ‘exit 7’; echo $?
7
$bash -c `exit 7`; echo $?
bash: -c: option requires an argument
2
$bash -c ‘exit 7’; echo $?
7
$trap ‘echo $? > solve.txt’ exit 10
$cat solve.txt
0
$cat solve.txt
0
$bash -c ‘exit 11’; echo $?
11
$
[/bash]

Indicate how each name would be interpreted if used as a command name

$type -a locate
locate is /usr/bin/locate
$type -a ls
ls is aliased to `ls --color=auto'
ls is /bin/ls
$type -t ls
alias
$type -t locate
file
$type -t /dev/urandom
$type -t /dev/sda1
$type -t urandom
$type -t sda1
$type -t type
builtin
$type -t shuf
file
$type -t bash
file
$type -t proc
$type -t debugfs
$sudo type -t debugfs
[sudo] password for jeffrin: 
sudo: type: command not found
$sudo type -t debugfs
sudo: type: command not found
$

fold: Wrap input lines to fit in specified width

$cat test.pl
use strict;
use File::Rename ();
use Pod::Usage;

main() unless caller;

sub main {
    my $options = File::Rename::Options::GetOptions
        or pod2usage;

    mod_version() if $options->{show_version};
    pod2usage( -verbose => 2 ) if $options->{show_manual};
    pod2usage( -exitval => 1 ) if $options->{show_help};

    @ARGV = map {glob} @ARGV if $^O =~ m{Win}msx;

    File::Rename::rename(\@ARGV, $options);
}

sub mod_version {
    print __FILE__ .
	' using File::Rename version '.
        $File::Rename::VERSION ."\n\n";
    exit 0
}   

1;

__END__

$

$fold  -w 10 -b  test.pl > part1.txt
$fold  -w 10   test.pl > part2.txt
$diff -u part1.txt part2.txt 
--- part1.txt	2018-03-15 22:50:38.084905051 +0530
+++ part2.txt	2018-03-15 22:50:48.768963638 +0530
@@ -55,10 +55,10 @@
 rsion {
     print 
 __FILE__ .
-	' using F
-ile::Renam
-e version 
-'.
+	' 
+using File
+::Rename v
+ersion '.
         $F
 ile::Renam
 e::VERSION