Complex Commands in Linux

                    Few complex linux commands in linux, like  xargs, find, expr.

find

-exec COMMAND \;

Carries out COMMAND on each file that find matches. The command sequence terminates with ; (the ";" is escaped to make certain the shell passes it to find literally, without interpreting it as a special character).

bash$ find ~/ -name '*.txt' /home/bozo/.kde/share/apps/karm/karmdata.txt /home/bozo/misc/irmeyc.txt /home/bozo/test-scripts/1.txt

If COMMAND contains {}, then find substitutes the full path name of the selected file for "{}".

find ~/ -name 'core*' -exec rm {} \; # Removes all core dump files from user's home directory.

find /home/bozo/projects -mtime 1 # Lists all files in /home/bozo/projects directory tree #+ that were modified within the last day. # # mtime = last modification time of the target file # ctime = last status change time (via 'chmod' or otherwise) # atime = last access time DIR=/home/bozo/junk_files find "$DIR" -type f -atime +5 -exec rm {} \; # ^^ # Curly brackets are placeholder for the path name output by "find." # # Deletes all files in "/home/bozo/junk_files" #+ that have not been accessed in at least 5 days. # # "-type filetype", where # f = regular file # d = directory # l = symbolic link, etc. # (The 'find' manpage and info page have complete listings.)

find /etc -exec grep '[0-9][0-9]*[.][0-9][0-9]*[.][0-9][0-9]*[.][0-9][0-9]*' {} \; # Finds all IP addresses (xxx.xxx.xxx.xxx) in /etc directory files. # There a few extraneous hits. Can they be filtered out? # Possibly by: find /etc -type f -exec cat '{}' \; | tr -c '.[:digit:]' '\n' \ | grep '^[^.][^.]*\.[^.][^.]*\.[^.][^.]*\.[^.][^.]*$' # # [:digit:] is one of the character classes #+ introduced with the POSIX 1003.2 standard. # Thanks, Stéphane Chazelas.

The -exec option to find should not be confused with the exec shell builtin.

Example 15-3. Badname, eliminate file names in current directory containing bad characters and whitespace.

#!/bin/bash # badname.sh # Delete filenames in current directory containing bad characters. for filename in * do badname=`echo "$filename" | sed -n /[\+\{\;\"\\\=\?~\(\)\<\>\&\*\|\$]/p` # badname=`echo "$filename" | sed -n '/[+{;"\=?~()<>&*|$]/p'` also works. # Deletes files containing these nasties: + { ; " \ = ? ~ ( ) < > & * | $ # rm $badname 2>/dev/null # ^^^^^^^^^^^ Error messages deep-sixed. done # Now, take care of files containing all manner of whitespace. find . -name "* *" -exec rm -f {} \; # The path name of the file that _find_ finds replaces the "{}". # The '\' ensures that the ';' is interpreted literally, as end of command. exit 0 #--------------------------------------------------------------------- # Commands below this line will not execute because of _exit_ command. # An alternative to the above script: find . -name '*[+{;"\\=?~()<>&*|$ ]*' -maxdepth 0 \ -exec rm -f '{}' \; # The "-maxdepth 0" option ensures that _find_ will not search #+ subdirectories below $PWD. # (Thanks, S.C.)

Example 15-4. Deleting a file by its inode number

#!/bin/bash # idelete.sh: Deleting a file by its inode number. # This is useful when a filename starts with an illegal character, #+ such as ? or -. ARGCOUNT=1 # Filename arg must be passed to script. E_WRONGARGS=70 E_FILE_NOT_EXIST=71 E_CHANGED_MIND=72 if [ $# -ne "$ARGCOUNT" ] then echo "Usage: `basename $0` filename" exit $E_WRONGARGS fi if [ ! -e "$1" ] then echo "File \""$1"\" does not exist." exit $E_FILE_NOT_EXIST fi inum=`ls -i | grep "$1" | awk '{print $1}'` # inum = inode (index node) number of file # ----------------------------------------------------------------------- # Every file has an inode, a record that holds its physical address info. # ----------------------------------------------------------------------- echo; echo -n "Are you absolutely sure you want to delete \"$1\" (y/n)? " # The '-v' option to 'rm' also asks this. read answer case "$answer" in [nN]) echo "Changed your mind, huh?" exit $E_CHANGED_MIND ;; *) echo "Deleting file \"$1\".";; esac find . -inum $inum -exec rm {} \; # ^^ # Curly brackets are placeholder #+ for text output by "find." echo "File "\"$1"\" deleted!" exit 0

The find command also works without the -exec option.

#!/bin/bash # Find suid root files. # A strange suid file might indicate a security hole, #+ or even a system intrusion. directory="/usr/sbin" # Might also try /sbin, /bin, /usr/bin, /usr/local/bin, etc. permissions="+4000" # suid root (dangerous!) for file in $( find "$directory" -perm "$permissions" ) do ls -ltF --author "$file" done

Its manpage provides more detail on this complex and powerful command.

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