bash built-in

sed 's/foo/bar/'                    # replaces only 1st instance in a line
sed 's/foo/bar/4'                   # replaces only 4th instance in a line
sed 's/foo/bar/g'                   # replaces ALL instances in a line
sed 's/\(.*\)foo\(.*foo\)/\1bar\2/' # replace the next-to-last case
sed 's/\(.*\)foo/\1bar/'            # replace only the last case

sed '/baz/s/foo/bar/g'

sed '/baz/!s/foo/bar/g'

sed 's/scarlet/red/g;s/ruby/red/g;s/puce/red/g'   # most seds
gsed 's/scarlet\|ruby\|puce/red/g'                # GNU sed only

ls -ld $(find .)    # ls recursif

find /var -iname "*.log"                        # Lister les fichiers nommés *.log dans /var (-iname: ignore case)
find /var -iname "*.log" 2> /dev/null           # Ignorer les erreurs "permission non accordée"
find ~/Téléchargements -size +20M -size -40M    # Taille entre 10 et 20 Mo

find /var/log/ -atime -1      # fichiers modfiés il y a moins de 1 jour (aujourd'hui)
find /var/log/ -atime +90     # fichiers modfiés il y a plus de 90 jours

find /tmp -type f -name "*.log" -exec chown adrien {} \;    # Executer une commande: {} est remplacé par le nom de fichier. 
find /tmp -type f -name "*.log" -exec rm -i {} \;

-atime : date d'accès  
-ctime : date de création  
-mtime : date de modification  
-type d : directory  
-type f : file  
-empty : fichier/dossier vide

[find with xarg and exec](https://www.grymoire.com/Unix/Find.html)

options
-------
-i case insensitive
-H show filename
-n show line numbers
-v reverse regex pattern (find lines not containing)

search string in files
----------------------
grep 'hello.*world' *.log       # list all lines containing "Hello, world" (-i ignore case)
grep -r 'foo' /home/mydir       # search recursively in mydir/
grep -rni "text" *              # search recursively in current dir. non case sensitive. print line numbers.
grep -C 2 'foo' test*.log       # print context around the match

regular expressions
-------------------
grep '^fred' /etc/passwd             # find 'fred', but only at the start of a line
grep '[FG]oo' *                      # find Foo or Goo in all files in the current dir
grep '[0-9][0-9][0-9]' *             # find all lines in all files in the current dir with three numbers in a row

find /tmp -print | xargs ls -ld
ls -ld `find /tmp -print`

mkdir -pv # create parent directory (verbose)

netstat -nat|grep -i ":80"|wc -l    # connections sur le port 80

ls -c1 | xargs -I {} mv {} "prefixe{}suffixe"

history | awk '{print $2;}' | sort | uniq -c | sort -rn | head -10

> Overwrite  
>> Append  
command >file or command 1>file # Redirect stdout to file. stderr to console  
command 2>file                  # Redirect stderr to file. stderr to console  
command >file                   # Redirect stdout to file. stderr to console  
command >file 2>&1              # Redirect stdout & stderr to file  
command 2>&1 | tee -a file      # Redirect stdout & stderr console and append to file 
command >/dev/null 2>&1         # Discard both stdout & stderr

find . -empty -type d

find . -empty -type d -delete

find . -type f -name "motif" -print | xargs rm -f

find . -type f -name '*.sql' | xargs grep 'foo.bar'

find /path/to/base/dir -type d -print0 | xargs -0 chmod 755

find /path/to/base/dir -type d -exec chmod 755 {} +

find /path/to/base/dir -type f -print0 | xargs -0 chmod 644

find /path/to/base/dir -type f -exec chmod 644 {} +