Some of the better shellscript scripts

1. Variables and Replacements

#!/bin/bash# variable Substitution# In addition, there are many other syntax for variable substitution# For example, b=${a/23/bb} replaces 23 with BB and so on, and then uses the time to findA=375hello= $a# Note Spaces# If there are spaces in the variable, then the variable needs to be enclosed in double quotes.hello="A b c D"Echo $hello# output A b c DEcho ${hello}# output A b c DEcho"$hello" # output A b c D# -------------------------------------------------# variable Assignment# When the variable is "naked" there is no variable symbol, and when it is assigned,#+ instead of being quoted.A=123# Use let to assign valuesLet A=16+5# It is best to write the Let form in the following format, because such a format will show that the assignment statement is a wholeLet"A=16+5"Echo $a# results are displayed# If you don't use let, direct a=16+5, then echo $a is 16+5# variable assignment in a for loop forAinch7 8 9 10do Echo-n"$a"Doneechoecho# Special variable assignment, assigning the result of the command to the variableA= ' Ls-l ' echo $aecho"$a"# The same as the meaning abovea=$ (uname-m) echo $aexit 0

2. Test structure of the individual recommendation

#!/bin/bash # [] Single bracket if -ne 0]then "This is not    root." Fi# [[]] double brackets if"integer" ]]then    "test"fi# Note, use [[]] instead of [], Be able to block many logic errors in the script, for example, although an error will be given in [],#+ However, the &&,| |,<> operation can still work in a [[]].    # Arithmetic test using (()) ((0))   # return 1 ((1))   # return 0, this is true ((5 > 4))  # return 0, this is true # Compare here are a lot of key parameters, such as-e,-eq, etc., Time to confirm # and or non-bottom equivalent notation [[Condition1 && Condition2]] if "$exp 1" "$exp 2" ] Fiexit 0

3. An arithmetic expression for personal recommendation

#!/bin/bash "n++"  # 101Echo $n ((n++)    # 102Echo $nexit 0

4. Clear the files in the directory

#!/bin/bash# Clean up version 1# ---------------------------------------------------------------------------------Cd/tmp/logcat/dev/null > Testfileecho"Log clean up."# Clean up version 2# ---------------------------------------------------------------------------------LOG_DIR=/TMP/LOGCD $LOG _dircat/dev/null > Testfileecho"Log clean up."Exit#clean up version 3# ---------------------------------------------------------------------------------log_dir=/tmp/logroot_uid=0lines=10e_xcd=66e_notroot=67if["$UID" -ne "$ROOT _uid"]then Echo"must is root to run this script."Exit $E _notrootElseEcho"Yes, you are the god root."Fiif[-N"$"]then lines=$1Elselines= $LINESfi# e_wrongagrs=65# case "$" in# "") lines=50;;# *[!0-9]*) echo "Usage: ' basename $ ' file-to-cleanup"; Exit $E _wrongagrs;;# *) lines=$1;CD $LOG _dirif[' pwd '! ="$LOG _dir"]then:echo"Can ' t change to $LOG _dir."Exit $E _XCDFI# More efficient implementation of the above content.# Cd/tmp/log | | {# echo "Cannot change to necessary directory." >&2# exit $E _xcd;# }tail-$lines testfile > MESG.TEMPMV mesg.temp messageecho"Logs cleaned up."Exit 0

5. The logic of personal referrals and, or

#!/bin/bash  # logic with  if  [Condition1] && [condition2]fiif  [[Condition1 && Condition2]]FI
   
    # logic or  
    if  [Condition1] | | [Condition2]fi
    if  [condition1 | | condition2]]fi 
   

6. Greatest common Divisor

#!/bin/bash  # greatest common divisor  args=2e_badargs=65< Span class= "REM" ># parameter check  if  [$#-ne "$ARGS"]  then echo 
   
     "Usage: ' basename $ ' first-number second-number"  exit $E _badargsfigcd () {dividend=$1 D            Ivsor=$2 remainder=1 until [
     "$remainder"  
    -eq  0] Do    Let 
     "remainder= $dividend% $divsor"  dividend= $divsor divsor= $remainder Done}
    # in addition, about the function call  
    #+ defined a function, and then the bottom call, the argument is passed in the following way  GCD $ $2echo; echo 
     "GCD of $ and $ = $dividend" ; Echoexit 0 
   

Some of the better shellscript scripts