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chore: integrated notions from articles on bash

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This commit is contained in:
Michele Cereda
2023-05-28 13:04:11 +02:00
parent 620e98d6d7
commit ddfde0044f
6 changed files with 214 additions and 26 deletions
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5
.vscode/settings.json vendored
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@@ -50,12 +50,12 @@
"hadolint",
"helmfile",
"imager",
"Istio",
"istio",
"istioctl",
"jdupes",
"journalctl",
"kbfs",
"KEDA",
"keda",
"keepass",
"keybase",
"knockd",
@@ -84,6 +84,7 @@
"pkexec",
"polkit",
"portsnap",
"posix",
"poweroff",
"pvresize",
"radeon",

3
knowledge base/README.md
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@@ -7,7 +7,8 @@ This is the collection of all notes, reminders and whatnot I gathered during the
- Prefer keeping an 80 characters width limit in code blocks.<br/>
This improves readability on most locations.
- Always use an highlighting annotation when writing code blocks (default to `txt`).
- Always use an highlighting annotation when writing code blocks<br/>
Default to `txt` if none is available.
- Use `sh` as highlighting annotation instead of `shell` when writing shell snippets in code blocks.<br/>
The local renderer just displays them better like this.

34
knowledge base/awk.md
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@@ -1,9 +1,41 @@
# `awk`
## Table of contents <!-- omit in toc -->
1. [TL;DR](#tldr)
1. [Further readings](#further-readings)
## TL;DR
```sh
# Print only the 3rd column.
awk '{print $3}' sales.txt
cat sales.txt | awk '{print $3}'
# Print the 2nd and 3rd columns, separated with a comma.
awk '{print $2 ", " $3}' sales.txt
cat sales.txt | awk '{print $2 ", " $3}'
# Print the sum of the 2nd and 3rd columns.
awk '{print $2 + $3}' sales.txt
# Print only lines with a length of more than 20 characters.
awk 'length($0) > 20' sales.txt
# Print only lines where the value of the second column is greater than 100.
awk '$2 > 100' sales.txt
```
## Further readings
- [Print line only if number in third field is greater than X]
- [Printing the last column of a line in a file]
- [The essential Bash cheat sheet]
<!-- project's references -->
<!-- in-article references -->
<!-- internal references -->
<!-- external references -->
[print line only if number in third field is greater than x]: https://unix.stackexchange.com/questions/395588/print-line-only-if-number-in-third-field-is-greater-than-x#395593
[Printing the last column of a line in a file]: https://stackoverflow.com/questions/13046167/printing-the-last-column-of-a-line-in-a-file#13046224
[printing the last column of a line in a file]: https://stackoverflow.com/questions/13046167/printing-the-last-column-of-a-line-in-a-file#13046224
[the essential bash cheat sheet]: https://betterprogramming.pub/the-essential-bash-cheat-sheet-e1c3df06560

160
knowledge base/bash.md
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@@ -17,10 +17,100 @@
## TL;DR
Shortcuts:
| Shortcut | Action |
| ------------ | ------------------------------------------------------- |
| `!!` | Insert the previous command in the current prompt. |
| `Alt` + `.` | Insert the last argument in the current prompt. |
| `Ctrl` + `L` | Clear the terminal. |
| `Ctrl` + `R` | Search **backwards** in the history one step at a time. |
| `Ctrl` + `Z` | Send the current foreground task to background. |
Get help:
```sh
# Get a brief summary about commands.
help 'nano'
# Get detailed information about commands.
man 'parallel'
```
Session management:
```sh
# Clean the console.
clear
# Print the current directory.
pwd
# Change the current directory.
cd
cd /bin
cd ..
# Create local variables.
VAR_NAME="value"
# Convert local variables in environment ones.
export VAR_NAME
export VAR_NAME="value"
# Deletes variables.
unset MY_FRIENDS
# Add directories to the current executables locations.
export PATH="${PATH}:/home/user/bin"
export PATH="/home/user/bin:${PATH}"
# Show the path of executables in $PATH.
which 'redis-cli'
# Show the path, man pages, source code, etc of executables in $PATH.
whereis nano
# List existing aliases.
alias
# Create aliases.
alias redo='$(history -p !!)'
# Remove aliases.
unalias redo
# Print all environment variables.
env
# Print all local *and* environment variables.
set
( set -o posix ; set )
# Print exported variables only.
export -p
# Logout after 3 minutes of inactivity.
TMOUT=180
```
Piping:
```sh
# Use the output of a command as the input of another.
tail 'file.txt' | grep 'search'
# Save the output of command 'a' as 'file.txt'.
# This *overwrites* already existing files with that name.
a > 'file.txt'
# Append the output of command 'a' to 'file.txt'.
a >> 'file.txt'
```
Arrays:
```sh
# Declare arrays.
ARRAY=(
"first_element"
@@ -42,7 +132,11 @@ echo ${ARRAY: -1}
# Get a slice of 4 elements from an array.
# Start from the element with index number 2.
echo ${ARRAY:2:4}
```
Functions:
```sh
# Declare functions.
functionName () { … }
function functionName { … }
@@ -52,6 +146,43 @@ functionName () { command1 ; … ; command N ; }
# Get all the arguments in input.
echo $@
```
Error management:
```sh
# Run a command or function on exit, kill or error.
trap "rm -f $tempfile" EXIT SIGTERM ERR
trap function-name EXIT SIGTERM ERR
# Disable CTRL-C.
trap "" SIGINT
# Re-enable CTRL-C.
trap - SIGINT
```
Job control:
```sh
# Print a list of background tasks.
jobs
# Bring a background task in the foreground.
fg
fg 'task_number'
```
Other snippets:
```sh
# Copy and paste *on Linux*.
echo "Hello my friend!" | xclip \
&& xclip -o >> pasted_text.txt
# Copy and paste *on Darwin*.
echo "Hello my friend!" | pbcopy \
&& pbpaste >> pasted_text.txt
# Of all the arguments in input, return only those which are existing directories.
DIRECTORIES=()
@@ -64,22 +195,6 @@ for (( I = $# ; I >= 0 ; I-- )); do
fi
done
# Print all shell and environment variables.
( set -o posix ; set )
# Print exported variables only.
export -p
# Run a command or function on exit, kill or error.
trap "rm -f $tempfile" EXIT SIGTERM ERR
trap function-name EXIT SIGTERM ERR
# Disable CTRL-C.
trap "" SIGINT
# Re-enable CTRL-C.
trap - SIGINT
# Bash 3 and `sh` have no built-in means to convert case of a string, but the
# `awk`, `sed` or `tr` tools can be used instead.
echo $(echo "$name" | tr '[:upper:]' '[:lower:]' )
@@ -89,6 +204,11 @@ echo $(tr '[:upper:]' '[:lower:]' <<< "$name")
echo ${name,,}
echo ${name^^}
# Leverage brace expansion to write less duplicated stuff.
mv /tmp/readme.md{,.backup} # = mv /tmp/readme.md /tmp/readme.md.backup
cp a{1,2,3}.txt backup-dir # = cp a1.txt a2.txt a3.txt backup-dir
cp a{1..3}.txt backup-dir # = cp a1.txt a2.txt a3.txt backup-dir
# Add a clock to the top-right part of the terminal.
while sleep 1
do
@@ -99,7 +219,7 @@ do
done &
# Show a binary clock.
watch -n 1 'echo "obase=2; `date +%s`" | bc'
watch -n 1 'echo "obase=2; $(date +%s)" | bc'
# Fork bomb.
:(){ :|: & };:
@@ -249,14 +369,20 @@ echo $RECORDED
- [The Bash trap command]
- [Bash startup files loading order]
- [How to detect if a script is being sourced]
- [The essential Bash cheat sheet]
- [Speed up your command line navigation]
- [6 Bash tricks you can use daily]
<!-- internal references -->
[trap]: trap.md
<!-- external references -->
[6 bash tricks you can use daily]: https://medium.com/for-linux-users/6-bash-tricks-you-can-use-daily-a32abdd8b13
[bash startup files loading order]: https://youngstone89.medium.com/unix-introduction-bash-startup-files-loading-order-562543ac12e9
[how to detect if a script is being sourced]: https://stackoverflow.com/questions/2683279/how-to-detect-if-a-script-is-being-sourced#28776166
[speed up your command line navigation]: https://blog.jread.com/speed-up-your-command-line-navigation-d4050207f02c
[the bash trap command]: https://www.linuxjournal.com/content/bash-trap-command
[the essential bash cheat sheet]: https://betterprogramming.pub/the-essential-bash-cheat-sheet-e1c3df06560
[upper- or lower-casing strings]: https://scriptingosx.com/2019/12/upper-or-lower-casing-strings-in-bash-and-zsh/
<!-- FIXME -->

28
knowledge base/sort.md
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@@ -1,23 +1,35 @@
# Sort
## Table of contents <!-- omit in toc -->
1. [TL;DR](#tldr)
1. [Sort by the value in the last field](#sort-by-the-value-in-the-last-field)
1. [Sources](#sources)
## TL;DR
```sh
# Sort given lines.
sort path/to/file
sort 'path/to/file'
# Sort lines in reverse.
sort -r path/to/file
sort -r 'path/to/file'
# Sort lines numerically.
sort -n path/to/file
sort -n 'path/to/file'
# Sort lines and remove duplicates.
sort -u path/to/file
sort -u 'path/to/file'
# Sort lines in random order.
sort -R 'path/to/file'
# Sort lines numerically according to the value in the 3rd column.
sort -t $'\t' -k 3n,3 'path/to/file'
# Sort by the value in the last field.
awk 'BEGIN {FS=","; OFS="|"} {print $NF,$0}' file.txt \
| sort -n -t '|' | awk -F '|' '{print $NF}'
| sort -n -t '|' | awk -F '|' '{print $NF}'
```
## Sort by the value in the last field
@@ -45,5 +57,11 @@ awk 'BEGIN {FS=","; OFS="|"} {print $NF,$0}' file.txt \
## Sources
- [Sort a file in Unix based on the last field]
- [The essential Bash cheat sheet]
<!-- project's references -->
<!-- in-article references -->
<!-- internal references -->
<!-- external references -->
[sort a file in unix based on the last field]: http://www.unixcl.com/2010/11/sort-file-based-on-last-field-unix.html
[the essential bash cheat sheet]: https://betterprogramming.pub/the-essential-bash-cheat-sheet-e1c3df06560

10
knowledge base/uniq.md
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@@ -18,3 +18,13 @@ uniq -cu path/to/file
# Count duplicated lines only.
uniq -cd path/to/file
```
## Sources
- [The essential Bash cheat sheet]
<!-- project's references -->
<!-- in-article references -->
<!-- internal references -->
<!-- external references -->
[the essential bash cheat sheet]: https://betterprogramming.pub/the-essential-bash-cheat-sheet-e1c3df06560