Skip to content

Shell'o'rama Tips.md

Latest commit

 

History

History
191 lines (162 loc) · 6.32 KB

Shell'o'rama Tips.md

File metadata and controls

191 lines (162 loc) · 6.32 KB

Parsing input parameters with bash script

I still prefer python btw but this is a nice idea to parse input parameters with few lines of bash scripting

help_usage() {
    echo -e "\nSome kind of help for my script (--param1 <p1>, --filename <file>)\n"
    exit 1
}
## Parsing input params
if [[ $# -eq 0 ]]; then
    help_usage
fi
PARAM1="defaultvalue"
FILE="defaultfilename"
while [[ $# -gt 0 ]]; do
    case "$1" in
        -p|--param1)
            PARAM1="$2"
            shift        # Argument
            shift        # Value
            ;;
        -f|--filename)
            FILE="$2"
            shift        # Argument
            shift        # Value
            ;;
        *)
            help_usage
            ;;
    esac
done
# ... and there you have it ...

while not EOF do

Simple file loop without read statements so I can use them elsewhere

for line in $(cat ~/ben/filename); do echo "-->$line<-- (hit enter)"; read junk; done

Same as above but it gets an entire line at a time from a file

while IFS="" read -r LINE || [ -n "$LINE" ]; do
    echo ">>$LINE<<"
done <<< $(cat ~/ben/filename)

ls, list and count them

ls files in a dir and count them, quite useful when dealing with huge number of them

MYDIR=/home/ben
ls -la $MYDIR/ ; echo $((`ls -la /$MYDIR/|wc -l` -3 ))

# Or oneshot with an alias...

ls full path

ls to list files, awk to transform into fullpath filenames, grep to gather data from it.
Useful inside a container or when you don't have find with you

ls -R / 2>/dev/null | awk '
/:$/&&f{s=$0;f=0}
/:$/&&!f{sub(/:$/,"");s=$0;f=1;next}
NF&&f{ print s"/"$0 }' |grep WhatEverFileName

diff on directories and files

If you want to massively compare directories containing your source code or taking track of changes between different backups you can use one of these methods.

Method 1, an overview, see only what's different

# Compare two ./src directory within project (./dir) and its backup copy (./dir.backup)
diff -rq dir/src dir.backup/src | grep -E '\.(c|h)( |$)'
#> Then take a look at changes there reported as:
#>      Files dir/src/input.c and dir.backup/src/input.c differ

Method 2, I'm lazy show me commands I need when files differs

# almost the same but results are quite interesting
diff -r dir/src dir.backup/src | grep -E '\.(c|h)( |$)'
# You barely need to copy 'n' paste outputs to evaluate files singularly
#>      diff -r dir/src/input.c dir.backup/src/input.c
#>      diff -r dir/src/...

# even lazier... copy and paste commands directly and use meld with it (sed basics)
diff -r dir/src dir.backup/src | grep -E '\.(c|h)( |$)' | sed 's/diff -r/meld/'

# or evaluate them and their changes, one file at a time
diff -r dir/src/input.c dir.backup/src/input.c

Method 3, just use git !

git always saves the day with the special bonus that you can always use it.
This command is usable even if those directories are not part of a git repository, basically because git uses rsync and diff all the time, no matter if you're syncing with or without git repos, git diff does it for you

#
git diff --no-index dir/src dir.backup/src -- '*.c' '*.h'

Shell prompt colors

My favorite shell colors (gentoo rocks) on /etc/bash/bashrc, /etc/bash.bashrc or whatever your favorite Linux OS calls it

    # Shell prompt
    if [[ ${EUID} == 0 ]] ; then
        PS1='\[\033[01;31m\]\u@\h\[\033[01;34m\] \w \$\[\033[00m\] '
    else
        PS1='\[\033[01;32m\]\u@\h\[\033[01;34m\] \w \$\[\033[00m\] '
    fi
    # ls colors
    alias ls='ls --color=auto'

NOTE: Always use /etc/bash.bashrc.local file when sourced or called within /etc/bash.bashrc.
There are chances that your changes will be lost during system upgrades if you are not wise enough. Instead always use /etc/bash.bashrc.local when available

Shell separator-<hr> like command

# Print a separator until last column
printf '━%.0s' $(seq $COLUMNS)

# Same as above but preferred if seq is not fully supported
printf '%*s\n' "${COLUMNS:-$(tput cols)}" '' | tr ' ' -

After sending shutdown command, ssh session doesn't terminate

Debian does it by default with virtual machines, here's a simple solution

apt-get install libpam-systemd dbus

Killing remote shell

To kill a shell just type:

<RETURN>~.

Changing Window Title

export PROMPT_COMMAND='echo -ne "\033]0;SOME TITLE HERE\007"'

SSH Reverse tunnel

This tip has been proven to be a viable option to bypass firewall restrictions and have a SSH reverse tunnel opened on a remote site when needed. You just need to open a SSH tunnel FROM remote server TO your machine, later on you may safely connect to your own machine (localhost) and use that reverse tunnel. Just pick these two things:

SERVER SIDE

ssh -R 9999:localhost:22 sourceuser@[your.own.IP.public.address]

CLIENT SIDE

On your side (client) you may safely open a shell to yourself

ssh localhost -p 9999

and here it goes the reverse tunnel

'screen' utility scrollback buffer

If the screen scrollback buffer is too small you can enter command line mode in a running session by pressing Ctrl+A, ":", then issuing the command: "scrollback <num>".
Example: "scrollback 10000" to get a 10000 line buffer.
You can also set the default number of scrollback lines by adding:

defscrollback 10000

to your ~/.screenrc file.

Internet Check

Somewhat nice and eye catching when you've a 10000 lines terminal full of ping output

# Using Google but whatever other classic ip is fine too
ping 8.8.8.8 | sed -e 's/bytes from //' -e 's/Unreachable/Unreachable\r ❌ /' -e 's/ ms/ ms\r✅/'

Shell fork bomb

A classic to use where ulimit is not set :)

:(){ :|:& };:

Detect if a script has being sourced or executed

To force a script to be sourced instead of just plainly executed it's as easy as getting return evaluation inside it. If you need to necessarily source your.script.sh because you're, for example, exporting some variables you can barely add this one liner to check it.

# This line acts as a guard. It aborts the script if it's not sourced.
(return 0 2>/dev/null) || { echo "Error: This script must be sourced, not executed." >&2; exit 1; }