Added command examples from external blogs

knowledge base/bash.md

@@ -31,6 +31,21 @@ echo $(tr '[:upper:]' '[:lower:]' <<< "$name")
 # Bash 5 has a special parameter expansion for upper- and lowercasing strings.
 echo ${name,,}
 echo ${name^^}
+
+# Add a clock to the top-right part of the terminal.
+while sleep 1
+do
+  tput sc;
+  tput cup 0 $(($(tput cols)-29))
+  date
+  tput rc
+done &
+
+# Show a binary clock.
+watch -n 1 'echo "obase=2; `date +%s`" | bc'
+
+# Fork bomb.
+:(){ :|: & };:
 ```
 
 ## Startup files loading order

knowledge base/chmod.md

@@ -0,0 +1,18 @@
+# Chmod
+
+## TL;DR
+
+```sh
+# Copy permissions from another file.
+# Only available in GNU cp.
+chmod --reference 'reference-file' 'changed-file'
+```
+
+## Sources
+
+- [18 selected super-useful Linux one-liners]
+
+<!-- project's references -->
+<!-- internal references -->
+<!-- external references -->
+[18 selected super-useful linux one-liners]: https://medium.com/codex/18-selected-super-useful-linux-one-liners-398ba6d20f8c

knowledge base/curl.md

@@ -34,7 +34,11 @@ curl -o '/dev/null' -w '%{http_code}\n' -s -I 'http://example.com'
 curl --request 'PUT' 'http://example.com'
 
 # Specify headers.
-curl 'http://example.com' -H 'Content-Type:application/json' 'http://example.com'
+curl 'http://example.com' -H 'Content-Type:application/json'
+
+# Fail fast with no output.
+# Returns the HTTP error code.
+curl -f 'http://example.com'
 
 # Skip certificate validation.
 curl --insecure 'https://example.com'

knowledge base/find.md

@@ -5,79 +5,82 @@
 ```sh
 # Change the permissions of all files and directories in the current directory,
 # recursively.
-find . -type d -exec chmod 755 {} +
-find . -type f -exec chmod 644 {} +
+find . -type 'd' -exec chmod '755' {} +
+find . -type 'f' -exec chmod '644' {} +
 
 # Change the ownership of all files and directories owned by a specific user or
 # group, recursively.
-find . -type d -user harry -exec chown daisy {} +
-find . -type f -group users -exec chown :admin {} +
+find . -type 'd' -user 'harry' -exec chown 'daisy' {} +
+find . -type 'f' -group 'users' -exec chown ':admin' {} +
 
 # Delete all empty files and directories in the 'Documents' directory.
 find Documents -empty -delete               # recursively
-find Documents -maxdepth 1 -empty -delete   # non recursively
+find Documents -maxdepth '1' -empty -delete   # non recursively
 
 # Get the extensions of all files larger than 1MB.
-find . -type f -size +1M -exec basename {} \; | sed 's|.*\.||' | sort -u
+find . -type 'f' -size '+1M' -exec basename {} \; | sed 's|.*\.||' | sort -u
+
+# Find all files between 5 and 10 MB.
+find . -type 'f' -size '+5M' -size '-10M'
 
 # Find files last accessed exactly 5 hour ago.
-find . -type f -amin 300
-find . -type f -atime 5h
+find . -type 'f' -amin '300'
+find . -type 'f' -atime '5h'
 
 # Find files last modified in the last hour.
-find . -type f -mmin -60
-find . -type f -mtime -1h
+find . -type 'f' -mmin '-60'
+find . -type 'f' -mtime '-1h'
 
 # Find files created more than 2 days ago.
-find . -type f -ctime +2
+find . -type 'f' -ctime '+2'
 
 # Find all empty directories in a git repository that are not from git itself.
-find path/to/repo -type d -empty -not -path "./.git/*"
+find 'path/to/repo' -type 'd' -empty -not -path "./.git/*"
 
 # Find broken symlinks in the given directories, recursively.
-find dir/1 dir/n -type l -exec test ! -e {} \; -print
-find dir/1 dir/n -xtype l   # gnu find only
+find 'dir/1' 'dir/N' -type 'l' -exec test ! -e {} \; -print
+find 'dir/1' 'dir/N' -xtype 'l'   # gnu find only
 
 # Sort files by name, in numeric order, regardless of the directory they are in.
-find . -type f -o -type l \
+find . -type 'f' -o -type 'l' \
   | awk 'BEGIN {FS="/"; OFS="|"} {print $NF,$0}' \
   | sort --field-separator '|' --numeric-sort \
   | cut -d '|' -f2
 
 # Print quoted file paths.
 # %p is for path.
-find . -type f -printf '"%p"\n'
-find . -type f -printf "'%p'\n"
+find . -type 'f' -printf '"%p"\n'
+find . -type 'f' -printf "'%p'\n"
 
 # Sort files by size.
 # %s is for size, %p is for path.
-find . -type f -printf '%s %p\n' | sort -nr | head -50
+find . -type 'f' -printf '%s %p\n' | sort -nr | head -50
 
 # Find files which are executable but not readable.
-find /sbin /usr/sbin -executable -not -readable -print
+find '/sbin' '/usr/sbin' -executable -not -readable -print
 
 # Find files which are writable by either their owner or their group.
-find . -perm /220
-find . -perm /u+w,g+w
-find . -perm /u=w,g=w
+find . -perm '/220'
+find . -perm '/u+w,g+w'
+find . -perm '/u=w,g=w'
 
 # Find files which are writable by both their owner and their group.
-find . -perm -220
-find . -perm -g+w,u+w
+find . -perm '-220'
+find . -perm '-g+w,u+w'
 
 # Record set-user-ID files and directories into '/root/suid.txt', and large
 # files into 'big-files.txt'
 find / \
-  \( -perm -4000 -fprintf /root/suid.txt '%#m %u %p\n' \) , \
-  \( -size +100M -fprintf big-files.txt '%-10s %p\n' \)
+  \( -perm '-4000' -fprintf '/root/suid.txt' '%#m %u %p\n' \) , \
+  \( -size '+100M' -fprintf 'big-files.txt' '%-10s %p\n' \)
 
 # Show files with hard links.
-find . -type f -not -links 1
-find -type f -links +1
+find . -type 'f' -not -links '1'
+find -type 'f' -links '+1'
 
 # Show files hard linked to a given file.
 # GNU extension.
-find -samefile path/to/file
+find -samefile 'path/to/file'
 ```
 
 ## Time specifications

knowledge base/limit the cpu usage of a process.md

@@ -0,0 +1,13 @@
+# Limit the CPU usage of a process
+
+## TL;DR
+
+```sh
+sudo cpulimit -p 'process-id' -l 'cpu-percentage'
+```
+
+## Sources
+
+- [25 awesome linux command one-Liners]
+
+[25 awesome linux command one-liners]: https://betterprogramming.pub/25-awesome-linux-command-one-liners-9495f26f07fb

knowledge base/mount.md

@@ -19,6 +19,9 @@ mount -t 'cifs' -o 'username=DOMAIN\Administrator,seal,vers=3.0' \
 # Mount a NFS share
 mount -t 'nfs' 'server:/share_name' '/mount/point'
 mount -t 'nfs' -o 'nfsvers=3,nolock' 'server:/share_name' '/mount/point'
+
+# Mount a temporary RAM disk.
+mount -t tmpfs tmpfs '/mount/point' -o 'size=2048m'
 ```
 
 ## Further readings

knowledge base/ping.md

@@ -0,0 +1,17 @@
+# Ping
+
+## TL;DR
+
+```sh
+# Make a sound every time the server receives a packet.
+ping -i 120 -a 'ip-address'
+```
+
+## Sources
+
+- [18 selected super-useful Linux one-liners]
+
+<!-- project's references -->
+<!-- internal references -->
+<!-- external references -->
+[18 selected super-useful linux one-liners]: https://medium.com/codex/18-selected-super-useful-linux-one-liners-398ba6d20f8c

knowledge base/rm.md

@@ -0,0 +1,18 @@
+# Rm
+
+## TL;DR
+
+```sh
+# Remove all files but the ones specified.
+rm !('path/to/file')
+rm !(*.xls|*.slsx|*.csv)
+```
+
+## Sources
+
+- [18 selected super-useful Linux one-liners]
+
+<!-- project's references -->
+<!-- internal references -->
+<!-- external references -->
+[18 selected super-useful linux one-liners]: https://medium.com/codex/18-selected-super-useful-linux-one-liners-398ba6d20f8c

knowledge base/ssh.md

@@ -15,21 +15,22 @@
 eval `ssh-agent` && ssh-add
 
 # Create new keys.
-ssh-keygen -t rsa -b 4096
-ssh-keygen -t dsa
-ssh-keygen -t ecdsa -b 521
-ssh-keygen -t ed25519 -f ~/.ssh/keys/id_ed25519 -C test@winzoz
+ssh-keygen -t 'rsa' -b '4096'
+ssh-keygen -t 'dsa'
+ssh-keygen -t 'ecdsa' -b '521'
+ssh-keygen -t 'ed25519' -f ~/.ssh/keys/id_ed25519 -C 'test@winzoz'
 
 # Remove elements from the known hosts list.
-ssh-keygen -R "pi4.lan"
-ssh-keygen -R 192.168.1.237 -f .ssh/known_hosts
-ssh-keygen -R "raspberrypi.lan" -f "${HOME}/.ssh/known_hosts"
+ssh-keygen -R 'pi4.lan'
+ssh-keygen -R '192.168.1.237' -f '.ssh/known_hosts'
+ssh-keygen -R 'pi.lan' -f "${HOME}/.ssh/known_hosts"
 
 # Change the password of a key.
 ssh-keygen -f ~/.ssh/id_rsa -p
 
 # Mount a remote folder.
-sshfs nas.lan:/mnt/data Data -o auto_cache,reconnect,defer_permissions,noappledouble,volname=Data
+sshfs 'nas.lan:/mnt/data' 'Data' \
+  -o 'auto_cache,reconnect,defer_permissions,noappledouble,volname=Data'
 
 # List keys added to the agent by fingerprint.
 ssh-add -l
@@ -37,6 +38,9 @@ ssh-add -L   # full key in OpenSSH format
 
 # Authorize keys for passwordless access.
 ssh-copy-id -i ~/.ssh/id_rsa.pub user@nas.lan
+
+# Connect to an unreachable host tunnelling the session through a bastion.
+ssh -t 'bastion-host' ssh 'unreachable-host'
 ```
 
 ## Key Management
@@ -44,10 +48,10 @@ ssh-copy-id -i ~/.ssh/id_rsa.pub user@nas.lan
 Create a new key:
 
 ```sh
-ssh-keygen -t rsa -b 4096
-ssh-keygen -t dsa
-ssh-keygen -t ecdsa -b 521
-ssh-keygen -t ed25519 -f .ssh/id_ed25519 -C test@winzoz
+ssh-keygen -t 'rsa' -b '4096'
+ssh-keygen -t 'dsa'
+ssh-keygen -t 'ecdsa' -b '521'
+ssh-keygen -t 'ed25519' -f '.ssh/id_ed25519' -C 'test@winzoz'
 ```
 
 ```plaintext
@@ -75,9 +79,9 @@ The key's randomart image is:
 Remove a host from the list of known hosts:
 
 ```sh
-ssh-keygen -R "pi4.lan"
-ssh-keygen -R 192.168.1.237 -f .ssh/known_hosts
-ssh-keygen -R "raspberrypi.lan" -f ".ssh/known_hosts"
+ssh-keygen -R 'pi4.lan'
+ssh-keygen -R '192.168.1.237' -f '.ssh/known_hosts'
+ssh-keygen -R 'raspberrypi.lan' -f '.ssh/known_hosts'
 ```
 
 ```plaintext
@@ -109,14 +113,14 @@ sshfs -o $OPTIONS_LIST $HOST:$REMOTE_PATH $LOCAL_PATH
 ```
 
 ```sh
-sshfs user@nas.lan:/mnt/data Data -o auto_cache,reconnect,defer_permissions,noappledouble,volname=Data
+sshfs 'user@nas.lan:/mnt/data' 'Data' -o 'auto_cache,reconnect,defer_permissions,noappledouble,volname=Data'
 ```
 
 ### Installation
 
 ```sh
 # Mac OS X requires `macports`, since `brew` does not offer 'sshfs' anymore
-sudo port install sshfs
+sudo port install 'sshfs'
 ```
 
 ## Configuration