Perl: Split s String into lines

How to split a string into lines while preserving the trailing "\n":
my @a = split(/^/, $text);

Perl: How to capture STDOUT and the exit code

Capture the exit code but not STDOUT:
$status = system("command");

Capture STDOUT but not exit status:
$output = `command`;

Shell: Find and remove dead links

$ find -L -type l -exec rm -f {} \;

SSH: Login without password

Generate a pair of authentication keys, but do not enter a passphrase:
$ ssh-keygen -t rsa
$ ssh othermachine mkdir -p .ssh
$ cat .ssh/id_rsa.pub | ssh othermachine 'cat >> .ssh/authorized_keys'

Shell: What are lines which are repeated ?

$ cat file.txt
21421415
42657547
65765234
85685634
24246547
12336467
76545253
12336467
46565865
65464364
34668747
21421415
67475473
$ cat file.txt | sort | uniq -c | \
awk '{ if ($1 > 1) { print $2 } }'
12336467
21421415

Shell: Output the common lines of two text files

One way:
$ diff --side-by-side file_a file_b | grep -n -v "[|<>]"

Or using the command 'comm' (man comm for more details):
$ comm -12 file_a file_b

Git: Recovering Lost Commits with git reflog and reset

Reviewing lost commits

The reflog command will give you a good history of what’s been happening on the head of your branches. Run it, then find the line that refers to the state that you want to get back to:

$ git reflog
... snip ...
cf42fa2... HEAD@{84}: checkout: moving to master
73b9363... HEAD@{85}: commit: Don't symlink to themes on deployment.
547cc1b... HEAD@{86}: commit: Deploy to effectif.com web server.
1dc3298... HEAD@{87}: commit: Updated the theme.
18c3f51... HEAD@{88}: commit: Verify with Google webmaster tools.
26fbb9c... HEAD@{89}: checkout: moving to effectif
The latest entries appear at the top. You can work out which branch each change was made on by looking out for lines that say “checkout: moving to …”. Commits 88 through to 85 (they’re numbered in the second column of the output) were the commits that I’d lost; all I needed to do was to get them back.

Reverting a branch to an earlier state

In short, you need to switch to the correct branch (“effectif” in my case) and then do a hard reset. The --hard options sets the HEAD of the current branch back to the commit that you specify:

$ git checkout effectif
$ git reset --hard 73b9363