Easily find issues by searching: #<Issue ID>
Example: #1832
Easily find members by searching in: <username>, <first name> and <last name>.
Example: Search smith, will return results smith and adamsmith
-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
# ^ Note minus sign!
# Lists all files in /home/bozo/projects directory tree
#+ that were modified within the last day (current_day - 1).
#
find /home/bozo/projects -mtime 1
# Same as above, but modified *exactly* one day ago.
#
# 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 "$DIR" -type f -atime +5 -exec rm {} \;
# ^ ^^
# Curly brackets are placeholder for the path name output by "find."
#
# Deletes all files in "/home/bozo/junk_files"
#+ that have not been accessed in *at least* 5 days (plus sign ... +5).
#
# "-type filetype", where
# f = regular file
# d = directory
# l = symbolic link, etc.
#
# (The 'find' manpage and info page have complete option listings.)
find /etc -exec grep '[0-9][0-9]*[.][0-9][0-9]*[.][0-9][0-9]*[.][0-9][0-9]*' {} \;
# Finds all IP addresses (xxx.xxx.xxx.xxx) in /etc directory files.
# There a few extraneous hits. Can they be filtered out?
# Possibly by:
find /etc -type f -exec cat '{}' \; | tr -c '.[:digit:]' '\n' \
| grep '^[^.][^.]*\.[^.][^.]*\.[^.][^.]*\.[^.][^.]*$'
#
# [: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 16-3. 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 16-4. 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
See Example 16-30, Example 3-4, and Example 11-9 for scripts using find. Its manpage provides more detail on this complex and powerful command.
A filter for feeding arguments to a command, and also a tool for assembling the commands themselves. It breaks a data stream into small enough chunks for filters and commands to process. Consider it as a powerful replacement for backquotes. In situations where command substitution fails with a too many arguments error, substituting xargs often works. 1 Normally, xargs reads from stdin or from a pipe, but it can also be given the output of a file.
The default command for xargs is echo. This means that input piped to xargs may have linefeeds and other whitespace characters stripped out.
bash$ ls -l total 0 -rw-rw-r-- 1 bozo bozo 0 Jan 29 23:58 file1 -rw-rw-r-- 1 bozo bozo 0 Jan 29 23:58 file2 bash$ ls -l | xargs total 0 -rw-rw-r-- 1 bozo bozo 0 Jan 29 23:58 file1 -rw-rw-r-- 1 bozo bozo 0 Jan... bash$ find ~/mail -type f | xargs grep "Linux" ./misc:User-Agent: slrn/0.9.8.1 (Linux) ./sent-mail-jul-2005: hosted by the Linux Documentation Project. ./sent-mail-jul-2005: (Linux Documentation Project Site, rtf version) ./sent-mail-jul-2005: Subject: Criticism of Bozo's Windows/Linux article ./sent-mail-jul-2005: while mentioning that the Linux ext2/ext3 filesystem . . .
ls | xargs -p -l gzip gzips every file in current directory, one at a time, prompting before each operation.
Note that xargs processes the arguments passed to it sequentially, one at a time.
bash$ find /usr/bin | xargs file /usr/bin: directory /usr/bin/foomatic-ppd-options: perl script text executable . . .
An interesting xargs option is -n NN, which limits to NN the number of arguments passed.
ls | xargs -n 8 echo lists the files in the current directory in 8 columns.
Another useful option is -0, in combination with find -print0 or grep -lZ. This allows handling arguments containing whitespace or quotes.
find / -type f -print0 | xargs -0 grep -liwZ GUI | xargs -0 rm -f
grep -rliwZ GUI / | xargs -0 rm -f
Either of the above will remove any file containing "GUI". (Thanks, S.C.)
Or:
cat /proc/"$pid"/"$OPTION" | xargs -0 echo # Formats output: ^^^^^^^^^^^^^^^ # From Han Holl's fixup of "get-commandline.sh" #+ script in "/dev and /proc" chapter.
The -P option to xargs permits running processes in parallel. This speeds up execution in a machine with a multicore CPU.
#!/bin/bash ls *gif | xargs -t -n1 -P2 gif2png # Converts all the gif images in current directory to png. # Options: # ======= # -t Print command to stderr. # -n1 At most 1 argument per command line. # -P2 Run up to 2 processes simultaneously. # Thank you, Roberto Polli, for the inspiration.
Example 16-5. Logfile: Using xargs to monitor system log
#!/bin/bash # Generates a log file in current directory # from the tail end of /var/log/messages. # Note: /var/log/messages must be world readable # if this script invoked by an ordinary user. # #root chmod 644 /var/log/messages LINES=5 ( date; uname -a ) >>logfile # Time and machine name echo ---------------------------------------------------------- >>logfile tail -n $LINES /var/log/messages | xargs | fmt -s >>logfile echo >>logfile echo >>logfile exit 0 # Note: # ---- # As Frank Wang points out, #+ unmatched quotes (either single or double quotes) in the source file #+ may give xargs indigestion. # # He suggests the following substitution for line 15: # tail -n $LINES /var/log/messages | tr -d "\"'" | xargs | fmt -s >>logfile # Exercise: # -------- # Modify this script to track changes in /var/log/messages at intervals #+ of 20 minutes. # Hint: Use the "watch" command.
As in find, a curly bracket pair serves as a placeholder for replacement text.
Example 16-6. Copying files in current directory to another
#!/bin/bash
# copydir.sh
# Copy (verbose) all files in current directory ($PWD)
#+ to directory specified on command-line.
E_NOARGS=85
if [ -z "$1" ] # Exit if no argument given.
then
echo "Usage: `basename $0` directory-to-copy-to"
exit $E_NOARGS
fi
ls . | xargs -i -t cp ./{} $1
# ^^ ^^ ^^
# -t is "verbose" (output command-line to stderr) option.
# -i is "replace strings" option.
# {} is a placeholder for output text.
# This is similar to the use of a curly-bracket pair in "find."
#
# List the files in current directory (ls .),
#+ pass the output of "ls" as arguments to "xargs" (-i -t options),
#+ then copy (cp) these arguments ({}) to new directory ($1).
#
# The net result is the exact equivalent of
#+ cp * $1
#+ unless any of the filenames has embedded "whitespace" characters.
exit 0
Example 16-7. Killing processes by name
#!/bin/bash
# kill-byname.sh: Killing processes by name.
# Compare this script with kill-process.sh.
# For instance,
#+ try "./kill-byname.sh xterm" --
#+ and watch all the xterms on your desktop disappear.
# Warning:
# -------
# This is a fairly dangerous script.
# Running it carelessly (especially as root)
#+ can cause data loss and other undesirable effects.
E_BADARGS=66
if test -z "$1" # No command-line arg supplied?
then
echo "Usage: `basename $0` Process(es)_to_kill"
exit $E_BADARGS
fi
PROCESS_NAME="$1"
ps ax | grep "$PROCESS_NAME" | awk '{print $1}' | xargs -i kill {} 2&>/dev/null
# ^^ ^^
# ---------------------------------------------------------------
# Notes:
# -i is the "replace strings" option to xargs.
# The curly brackets are the placeholder for the replacement.
# 2&>/dev/null suppresses unwanted error messages.
#
# Can grep "$PROCESS_NAME" be replaced by pidof "$PROCESS_NAME"?
# ---------------------------------------------------------------
exit $?
# The "killall" command has the same effect as this script,
#+ but using it is not quite as educational.
Example 16-8. Word frequency analysis using xargs
#!/bin/bash # wf2.sh: Crude word frequency analysis on a text file. # Uses 'xargs' to decompose lines of text into single words. # Compare this example to the "wf.sh" script later on. # Check for input file on command-line. ARGS=1 E_BADARGS=85 E_NOFILE=86 if [ $# -ne "$ARGS" ] # Correct number of arguments passed to script? then echo "Usage: `basename $0` filename" exit $E_BADARGS fi if [ ! -f "$1" ] # Does file exist? then echo "File \"$1\" does not exist." exit $E_NOFILE fi ##################################################### cat "$1" | xargs -n1 | \ # List the file, one word per line. tr A-Z a-z | \ # Shift characters to lowercase. sed -e 's/\.//g' -e 's/\,//g' -e 's/ /\ /g' | \ # Filter out periods and commas, and #+ change space between words to linefeed, sort | uniq -c | sort -nr # Finally remove duplicates, prefix occurrence count #+ and sort numerically. ##################################################### # This does the same job as the "wf.sh" example, #+ but a bit more ponderously, and it runs more slowly (why?). exit $?
All-purpose expression evaluator: Concatenates and evaluates the arguments according to the operation given (arguments must be separated by spaces). Operations may be arithmetic, comparison, string, or logical.
expr 3 + 5
returns 8
expr 5 % 3
returns 2
expr 1 / 0
returns the error message, expr: division by zero
Illegal arithmetic operations not allowed.
expr 5 \* 3
returns 15
The multiplication operator must be escaped when used in an arithmetic expression with expr.
y=`expr $y + 1`
Increment a variable, with the same effect as let y=y+1 and y=$(($y+1)). This is an example of arithmetic expansion.
z=`expr substr $string $position $length`
Extract substring of $length characters, starting at $position.
Example 16-9. Using expr
#!/bin/bash # Demonstrating some of the uses of 'expr' # ======================================= echo # Arithmetic Operators # ---------- --------- echo "Arithmetic Operators" echo a=`expr 5 + 3` echo "5 + 3 = $a" a=`expr $a + 1` echo echo "a + 1 = $a" echo "(incrementing a variable)" a=`expr 5 % 3` # modulo echo echo "5 mod 3 = $a" echo echo # Logical Operators # ------- --------- # Returns 1 if true, 0 if false, #+ opposite of normal Bash convention. echo "Logical Operators" echo x=24 y=25 b=`expr $x = $y` # Test equality. echo "b = $b" # 0 ( $x -ne $y ) echo a=3 b=`expr $a \> 10` echo 'b=`expr $a \> 10`, therefore...' echo "If a > 10, b = 0 (false)" echo "b = $b" # 0 ( 3 ! -gt 10 ) echo b=`expr $a \< 10` echo "If a < 10, b = 1 (true)" echo "b = $b" # 1 ( 3 -lt 10 ) echo # Note escaping of operators. b=`expr $a \<= 3` echo "If a <= 3, b = 1 (true)" echo "b = $b" # 1 ( 3 -le 3 ) # There is also a "\>=" operator (greater than or equal to). echo echo # String Operators # ------ --------- echo "String Operators" echo a=1234zipper43231 echo "The string being operated upon is \"$a\"." # length: length of string b=`expr length $a` echo "Length of \"$a\" is $b." # index: position of first character in substring # that matches a character in string b=`expr index $a 23` echo "Numerical position of first \"2\" in \"$a\" is \"$b\"." # substr: extract substring, starting position & length specified b=`expr substr $a 2 6` echo "Substring of \"$a\", starting at position 2,\ and 6 chars long is \"$b\"." # The default behavior of the 'match' operations is to #+ search for the specified match at the BEGINNING of the string. # # Using Regular Expressions ... b=`expr match "$a" '[0-9]*'` # Numerical count. echo Number of digits at the beginning of \"$a\" is $b. b=`expr match "$a" '\([0-9]*\)'` # Note that escaped parentheses # == == #+ trigger substring match. echo "The digits at the beginning of \"$a\" are \"$b\"." echo exit 0
The : (null) operator can substitute for
match. For example, b=`expr $a : [0-9]*` is the exact equivalent of b=`expr match $a [0-9]*` in the above listing.
#!/bin/bash echo echo "String operations using \"expr \$string : \" construct" echo "===================================================" echo a=1234zipper5FLIPPER43231 echo "The string being operated upon is \"`expr "$a" : '\(.*\)'`\"." # Escaped parentheses grouping operator. == == # *************************** #+ Escaped parentheses #+ match a substring # *************************** # If no escaped parentheses... #+ then 'expr' converts the string operand to an integer. echo "Length of \"$a\" is `expr "$a" : '.*'`." # Length of string echo "Number of digits at the beginning of \"$a\" is `expr "$a" : '[0-9]*'`." # ------------------------------------------------------------------------- # echo echo "The digits at the beginning of \"$a\" are `expr "$a" : '\([0-9]*\)'`." # == == echo "The first 7 characters of \"$a\" are `expr "$a" : '\(.......\)'`." # ===== == == # Again, escaped parentheses force a substring match. # echo "The last 7 characters of \"$a\" are `expr "$a" : '.*\(.......\)'`." # ==== end of string operator ^^ # (actually means skip over one or more of any characters until specified #+ substring) echo exit 0
The above script illustrates how expr uses the escaped parentheses -- \( ... \) -- grouping operator in tandem with regular expression parsing to match a substring. Here is a another example, this time from "real life."
# Strip the whitespace from the beginning and end. LRFDATE=`expr "$LRFDATE" : '[[:space:]]*\(.*\)[[:space:]]*$'` # From Peter Knowles' "booklistgen.sh" script #+ for converting files to Sony Librie/PRS-50X format. # (http://booklistgensh.peterknowles.com)
Perl, sed, and awk have far superior string parsing facilities. A short sed or awk "subroutine" within a script (see Section 36.2) is an attractive alternative to expr.
See Section 10.1for more on using expr in string operations.