藍色情懷

[Unix/Linux/MacOS]

===============
find command
===============

#find . -name \*.[h,c] -exec grep -i RFC1213_SYS_INCLUDE {} /dev/null \;
#find . -name "*.[h,c]" -exec grep -i RFC1213_SYS_INCLUDE {} \; -print
#find . -name *.c -or -name *.h -exec grep "RFC1213_SYS_INCLUDE" {} \; -print
#find . -exec -name '*.pdf' -exec pdftotext {} \;   //find the pdf's files string pattern

======================================================================================
All hail the power of find!

The command:

  grep -i -l "dungarees" *.txt

could be rewritten,

 find . -name \*.txt -exec grep -i "dungarees" {} \; -print

This is making use of the result code the grep normally returns to the
shell. From here it is easy to reverse the logic of the grep test:

  find . -name \*.txt ! -exec grep -i "dungarees" {} \; -print

#
# A couple of refinements are possible.
#
# 1- grep can be silenced, so only the file names will be listed, by
#    giving grep the "-q" option (AIX or UNICOS) or "-s" option (IRIX).
#
# 2- find can be restricted to a search of the current working
#    directory using the -prune option.
#
# The following solution (AIX or UNICOS) was sent in by Dale Clark:
#

find * \( -type d -prune \) -o -name "*" ! -exec egrep -iq "valid until" {} \; -print


====================================================================================================
$ find . -name *.c -or -name *.h -exec grep "belong here" {} \;
* XXX doesn't really belong here I guess...
* This doesn't really belong here, but I can't think of a better
* XXX doesn't really belong here I guess...
* XXX FIXME: probably does not belong here
* XXX FIXME: probably does not belong here
/* XXX FIXME this does not belong here */
* XXX these don't really belong here; but for now they're

====================================================================================================

#find2.sh
#====================================================================================================
 if test $1
 then
 find . -type f -exec grep $1 /dev/null {} \;
 else
 echo "正確的語法為: ./find2 搜尋字詞? "
 fi
#====================================================================================================


Complex Commands

Commands for more advanced users

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

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

   1 find /home/bozo/projects -mtime 1
   2 #  Lists all files in /home/bozo/projects directory tree
   3 #+ that were modified within the last day.
   4 #
   5 #  mtime = last modification time of the target file
   6 #  ctime = last status change time (via 'chmod' or otherwise)
   7 #  atime = last access time
   8
   9 DIR=/home/bozo/junk_files
  10 find "$DIR" -type f -atime +5 -exec rm {} \;
  11 #  Deletes all files in "/home/bozo/junk_files"
  12 #+ that have not been accessed in at least 5 days.
  13 #
  14 #  "-type filetype", where
  15 #  f = regular file
  16 #  d = directory, etc.
  17 #  (The 'find' manpage has a complete listing.)

   1 find /etc -exec grep '[0-9][0-9]*[.][0-9][0-9]*[.][0-9][0-9]*[.][0-9][0-9]*' {} \;
   2
   3 # Finds all IP addresses (xxx.xxx.xxx.xxx) in /etc directory files.
   4 # There a few extraneous hits - how can they be filtered out?
   5
   6 # Perhaps by:
   7
   8 find /etc -type f -exec cat '{}' \; | tr -c '.[:digit:]' '\n' \
   9  | grep '^[^.][^.]*\.[^.][^.]*\.[^.][^.]*\.[^.][^.]*$'
  10 # [:digit:] is one of the character classes
  11 # introduced with the POSIX 1003.2 standard.
  12
  13 # Thanks, S.C.

    Note    

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

    Example 12-2. Badname, eliminate file names in current directory containing bad characters and whitespace.

   1 #!/bin/bash
   2
   3 # Delete filenames in current directory containing bad characters.
   4
   5 for filename in *
   6 do
   7 badname=`echo "$filename" | sed -n /[\+\{\;\"\\\=\?~\(\)\<\>\&\*\|\$]/p`
   8 # Files containing those nasties:     + { ; " \ = ? ~ ( ) < > & * | $
   9 rm $badname 2>/dev/null    # So error messages deep-sixed.
  10 done
  11
  12 # Now, take care of files containing all manner of whitespace.
  13 find . -name "* *" -exec rm -f {} \;
  14 # The path name of the file that "find" finds replaces the "{}".
  15 # The '\' ensures that the ';' is interpreted literally, as end of command.
  16
  17 exit 0
  18
  19 #---------------------------------------------------------------------
  20 # Commands below this line will not execute because of "exit" command.
  21
  22 # An alternative to the above script:
  23 find . -name '*[+{;"\\=?~()<>&*|$ ]*' -exec rm -f '{}' \;
  24 exit 0
  25 # (Thanks, S.C.)

    Example 12-3. Deleting a file by its inode number

   1 #!/bin/bash
   2 # idelete.sh: Deleting a file by its inode number.
   3
   4 #  This is useful when a filename starts with an illegal character,
   5 #+ such as ? or -.
   6
   7 ARGCOUNT=1                      # Filename arg must be passed to script.
   8 E_WRONGARGS=70
   9 E_FILE_NOT_EXIST=71
  10 E_CHANGED_MIND=72
  11
  12 if [ $# -ne "$ARGCOUNT" ]
  13 then
  14   echo "Usage: `basename $0` filename"
  15   exit $E_WRONGARGS
  16 fi  
  17
  18 if [ ! -e "$1" ]
  19 then
  20   echo "File \""$1"\" does not exist."
  21   exit $E_FILE_NOT_EXIST
  22 fi  
  23
  24 inum=`ls -i | grep "$1" | awk '{print $1}'`
  25 # inum = inode (index node) number of file
  26 # Every file has an inode, a record that hold its physical address info.
  27
  28 echo; echo -n "Are you absolutely sure you want to delete \"$1\" (y/n)? "
  29 # The '-v' option to 'rm' also asks this.
  30 read answer
  31 case "$answer" in
  32 [nN]) echo "Changed your mind, huh?"
  33       exit $E_CHANGED_MIND
  34       ;;
  35 *)    echo "Deleting file \"$1\".";;
  36 esac
  37
  38 find . -inum $inum -exec rm {} \;
  39 echo "File "\"$1"\" deleted!"
  40
  41 exit 0

    See Example 12-22, Example 3-4, and Example 10-9 for scripts using find. Its manpage provides more detail on this complex and powerful command.
xargs

    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 backquotes fail with a too many arguments error, substituting xargs often works. 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 29 23:58 file2
           

    ls | xargs -p -l gzip gzips every file in current directory, one at a time, prompting before each operation.
    Tip    

    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.
    Tip    

    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.)

    Example 12-4. Logfile using xargs to monitor system log

   1 #!/bin/bash
   2
   3 # Generates a log file in current directory
   4 # from the tail end of /var/log/messages.
   5
   6 # Note: /var/log/messages must be world readable
   7 # if this script invoked by an ordinary user.
   8 #         #root chmod 644 /var/log/messages
   9
  10 LINES=5
  11
  12 ( date; uname -a ) >>logfile
  13 # Time and machine name
  14 echo --------------------------------------------------------------------- >>logfile
  15 tail -$LINES /var/log/messages | xargs |  fmt -s >>logfile
  16 echo >>logfile
  17 echo >>logfile
  18
  19 exit 0
  20
  21 # Exercise:
  22 # --------
  23 #  Modify this script to track changes in /var/log/messages at intervals
  24 #+ of 20 minutes.
  25 #  Hint: Use the "watch" command.

    Example 12-5. copydir, copying files in current directory to another, using xargs

   1 #!/bin/bash
   2
   3 # Copy (verbose) all files in current directory
   4 # to directory specified on command line.
   5
   6 if [ -z "$1" ]   # Exit if no argument given.
   7 then
   8   echo "Usage: `basename $0` directory-to-copy-to"
   9   exit 65
  10 fi  
  11
  12 ls . | xargs -i -t cp ./{} $1
  13 # This is the exact equivalent of
  14 #    cp * $1
  15 # unless any of the filenames has "whitespace" characters.
  16
  17 exit 0

expr

    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 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 12-6. Using expr

   1 #!/bin/bash
   2
   3 # Demonstrating some of the uses of 'expr'
   4 # =======================================
   5
   6 echo
   7
   8 # Arithmetic Operators
   9 # ---------- ---------
  10
  11 echo "Arithmetic Operators"
  12 echo
  13 a=`expr 5 + 3`
  14 echo "5 + 3 = $a"
  15
  16 a=`expr $a + 1`
  17 echo
  18 echo "a + 1 = $a"
  19 echo "(incrementing a variable)"
  20
  21 a=`expr 5 % 3`
  22 # modulo
  23 echo
  24 echo "5 mod 3 = $a"
  25
  26 echo
  27 echo
  28
  29 # Logical Operators
  30 # ------- ---------
  31
  32 #  Returns 1 if true, 0 if false,
  33 #+ opposite of normal Bash convention.
  34
  35 echo "Logical Operators"
  36 echo
  37
  38 x=24
  39 y=25
  40 b=`expr $x = $y`         # Test equality.
  41 echo "b = $b"            # 0  ( $x -ne $y )
  42 echo
  43
  44 a=3
  45 b=`expr $a \> 10`
  46 echo 'b=`expr $a \> 10`, therefore...'
  47 echo "If a > 10, b = 0 (false)"
  48 echo "b = $b"            # 0  ( 3 ! -gt 10 )
  49 echo
  50
  51 b=`expr $a \< 10`
  52 echo "If a < 10, b = 1 (true)"
  53 echo "b = $b"            # 1  ( 3 -lt 10 )
  54 echo
  55 # Note escaping of operators.
  56
  57 b=`expr $a \<= 3`
  58 echo "If a <= 3, b = 1 (true)"
  59 echo "b = $b"            # 1  ( 3 -le 3 )
  60 # There is also a "\>=" operator (greater than or equal to).
  61
  62
  63 echo
  64 echo
  65
  66 # Comparison Operators
  67 # ---------- ---------
  68
  69 echo "Comparison Operators"
  70 echo
  71 a=zipper
  72 echo "a is $a"
  73 if [ `expr $a = snap` ]
  74 # Force re-evaluation of variable 'a'
  75 then
  76    echo "a is not zipper"
  77 fi   
  78
  79 echo
  80 echo
  81
  82
  83
  84 # String Operators
  85 # ------ ---------
  86
  87 echo "String Operators"
  88 echo
  89
  90 a=1234zipper43231
  91 echo "The string being operated upon is \"$a\"."
  92
  93 # length: length of string
  94 b=`expr length $a`
  95 echo "Length of \"$a\" is $b."
  96
  97 # index: position of first character in substring
  98 #        that matches a character in string
  99 b=`expr index $a 23`
 100 echo "Numerical position of first \"2\" in \"$a\" is \"$b\"."
 101
 102 # substr: extract substring, starting position & length specified
 103 b=`expr substr $a 2 6`
 104 echo "Substring of \"$a\", starting at position 2,\
 105 and 6 chars long is \"$b\"."
 106
 107
 108 #  The default behavior of the 'match' operations is to
 109 #+ search for the specified match at the ***beginning*** of the string.
 110 #
 111 #        uses Regular Expressions
 112 b=`expr match "$a" '[0-9]*'`               #  Numerical count.
 113 echo Number of digits at the beginning of \"$a\" is $b.
 114 b=`expr match "$a" '\([0-9]*\)'`           #  Note that escaped parentheses
 115 #                   ==      ==              + trigger substring match.
 116 echo "The digits at the beginning of \"$a\" are \"$b\"."
 117
 118 echo
 119
 120 exit 0

    Important    

    The : 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.

   1 #!/bin/bash
   2
   3 echo
   4 echo "String operations using \"expr \$string : \" construct"
   5 echo "==================================================="
   6 echo
   7
   8 a=1234zipper5FLIPPER43231
   9
  10 echo "The string being operated upon is \"`expr "$a" : '\(.*\)'`\"."
  11 #     Escaped parentheses grouping operator.            ==  ==
  12
  13 #       ***************************
  14 #+          Escaped parentheses
  15 #+           match a substring
  16 #       ***************************
  17
  18
  19 #  If no escaped parentheses...
  20 #+ then 'expr' converts the string operand to an integer.
  21
  22 echo "Length of \"$a\" is `expr "$a" : '.*'`."   # Length of string
  23
  24 echo "Number of digits at the beginning of \"$a\" is `expr "$a" : '[0-9]*'`."
  25
  26 # ------------------------------------------------------------------------- #
  27
  28 echo
  29
  30 echo "The digits at the beginning of \"$a\" are `expr "$a" : '\([0-9]*\)'`."
  31 #                                                             ==      ==
  32 echo "The first 7 characters of \"$a\" are `expr "$a" : '\(.......\)'`."
  33 #         =====                                          ==       ==
  34 # Again, escaped parentheses force a substring match.
  35 #
  36 echo "The last 7 characters of \"$a\" are `expr "$a" : '.*\(.......\)'`."
  37 #         ====                  end of string operator  ^^
  38 #  (actually means skip over one or more of any characters until specified
  39 #+  substring)
  40
  41 echo
  42
  43 exit 0

This example illustrates how expr uses the escaped parentheses -- \( ... \) -- grouping operator in tandem with regular expression parsing to match a substring.

Perl, sed, and awk have far superior string parsing facilities. A short sed or awk "subroutine" within a script (see Section 34.2) is an attractive alternative to using expr.

See Section 9.2 for more on string operations.