Bash Index : R - The 'R' Bash commands : description, flags and examples

This can be done by specifying several variables when calling read :

• string='foo bar baz'; read a b c <<< "$string"; echo "$a $b $c"
• text='one two three'; read -r col1 col2 col3 <<< "$text"; printf "col1: %s, col2: %s, col3: %s\n" "$col1" "$col2" "$col3"

This will transpose this :

a
b
c

z

into this :

a	b	c
d	e	f
g	
y	z

• ps -o nice PID
• top -p PID

sleep 3 & renice 5 -p $!

[1] 19145
19145 (process ID) old priority 0, new priority 5

sleep 3 & renice -n 5 -p $!

[1] 19167
19167 (process ID) old priority 0, new priority 5

Same as above since -n is optional.

sleep 3 & renice 5 -p $!; renice 5 -p $!

[1] 19208
19208 (process ID) old priority 0, new priority 5
19208 (process ID) old priority 5, new priority 5

You can not renice an already reniced process (or at least, not like this).

sleep 3 & renice +5 -p $!; renice +5 -p $!

[1] 19251
19251 (process ID) old priority 0, new priority 5
19251 (process ID) old priority 5, new priority 5

The + sign seems to make no big difference.

sleep 3 & renice 5 -p $!; renice 1 -p $!

[1] 19272
19272 (process ID) old priority 0, new priority 5
renice: failed to set priority for 19272 (process ID): Permission denied

• The value we specify is NOT an increment, it's the expected value (see this example).
• Only root can decrease a nice value (i.e. give higher priority to a process).

sleep 3 & renice 5 -p $!; renice 6 -p $!

[1] 20538
20538 (process ID) old priority 0, new priority 5
20538 (process ID) old priority 5, new priority 6

• cd directory; find . -name '*' -type f | xargs rm
• cd directory; find . -name '*' -type f -delete

The regular expressions have a callback syntax to refer to a "previously matched substring". In other tools (sed, Emacs, Vi, ...), such callbacks are written \n (n being the number of the matched expression, starting at 1). Even though rename accepts this syntax, it will complain saying it prefers them specified using the $ sign : $n. Example :

Let's consider the set of files produced by :

prefix='testFile_'; extension='.ext'; for i in {1..20}; do touch "$prefix$i$extension"; done

For the files 1 to 9 to be numbered 01 to 09, just run :

prefix='testFile_'; rename 's/_([0-9]\.)/_0$1/g' $prefix*

• $prefix is used to avoid affecting all files with a rename regExp *
• the substring to match for re-use must be enclosed by ( ) (no need to escape parens), and is recalled as $n (not \n), n being the n^th matched substring

Let's consider a collection of files :

• file names are not consistent
• extensions are not consistent either : mp3/MP3, jpg/jpeg/JPG, ...
• files have no numbering
• the relative numbers of files are not important

... in which we would like to decrease entropy. To do so, let's :

• rename files based on a pattern
• number files

Let's do it with :

• files downloaded from YouTube are named after artist - title - [youtubeVideoID].webm, and we'd like the [youtubeVideoID] part out (including brackets and leading space) :
  rename 's/ \[[^\]]+]//' *webm highlighted brackets are those above
• add missing hyphen to change nn name.extension into nn - name.extension
  rename -n 's/^([0-9]{2} )/$1- /' *extension
• remove suffix from filename with a trailing UUID / random suffix, such as description-of-whats-inside-XyZ123.extension
  rename 's/-[A-Za-z0-9]{6}\././' *extension
• remove duplicate marker from filename : someFile(n).extension
  rename 's/\([0-9]\)\././' *extension
• rename <32>_<8>.extension files into <8>.extension : like c11494a588c0d65b094a094a588c0d6588c0d6f8380a90c2ab1_f46f29ba.extension into f46f29ba.extension
  rename 's/^[0-9a-zA-Z]{32}_([0-9a-zA-Z]{8}\.[a-z]{3,4})/$1/' *extension
• change filename case :
  touch MYFILE_123; rename 'y/A-Z/a-z/' *123; ls -1 *123; rename 'y/a-z/A-Z/' *123; ls -1 *123

  myfile_123
  MYFILE_123

  This works only on case-sensitive filesystems, where MYFILE and myfile are distinct files which can co-exist in a single directory (hack required otherwise , read below).
  If working on a FAT32 volume (aka vfat) where MYFILE and myfile are the same file, the idea would be to :

  1. rename MYFILE into myfile_someArbitrarySuffix
  2. then change myfile_someArbitrarySuffix into myfile

  Let's give this a try :

  1. initialize things :
     suffix='_lowercase'; touch MYFILE.EXTENSION; ll
  2. change filename case :
     • rename 'y/A-Z/a-z/; s/^(.*)$/$1'$suffix'/' * && rename 's/^(.*)'$suffix'$/$1/' *"$suffix"
     • rename "y/A-Z/a-z/; s/^(.*)\$/\$1$suffix/" * && rename "s/^(.*)$suffix\$/\$1/" *"$suffix"
  3. clean before leaving :
     ll; rm myfile.extension

  Both commands return:

  -rwxrwx--- 1 root 98 0 nov.   7 16:43 MYFILE.EXTENSION
  -rwxrwx--- 1 root 98 0 nov.   7 16:43 myfile.extension