A little test of the operation and maintenance shell script (10): the shift built-in command reads multiple command line parameters

1: Read positional parameters

Using shift [n], you can read multiple positional parameters; it is more convenient to use case for a single command line parameter; but multiple command line parameters are not reasonable. Use the command shift command to get the command line parameters one by one in the variable, shift It is a built-in command in Bash. This command is used to shift the passed parameter variable to the left. Its syntax: shift [n]; n is a non-negative integer less than or equal to "$#". If 0, the positional argument will not be changed; if not specified, it will be set to 1 by default. If n is greater than $#, the positional parameters will not change. If n is greater than $# or less than 0, the status code of this status will be greater than 0, otherwise it will be 0;

[root@www standandinout]# cat shiftreadparam.sh
#!/bin/bash -
#================================ ================================================== =================================
#
#
# FILE: shiftreadparam.sh
# USAGE: ./shiftreadparam.sh
# DESCRIPTION: Read positional parameters: Use shift [n] to read multiple positional parameters; it is more convenient to use case for a single command line parameter; but multiple command line parameters are not reasonable, use the command shift command to read one after another in the variable Get the command line parameters directly.
# shift is a built-in command in Bash. This command is used to shift the passed parameter variable to the left. Its syntax: shift [n]; n is a non-negative integer less than or equal to "$#". If 0, the positional parameter will not be changed;
# If not specified, it will be set to 1 by default. If n is greater than $#, the positional parameters will not change.
# If n is greater than $# or less than 0, the status code of this status will be greater than 0, otherwise it will be 0; # # #
OPTIONS
:
-------
# REQUIREMENTS: ---------
#
# BUGS: ------
# NOTES: --------
# AUTHOR: ---------YangGe (TOM) , [email protected]
# ORGANIZATION:
# CREATED: 2023-8-24 09:11:20
# REVISION: --------
#
#
#
#
#
#========== ================================================== ================================================== ======
flag=0
# If the number of command line parameters is not 0, continue the while loop, otherwise exit the loop
while [ $# -ne 0 ]
do

# Print the value of special variable $1 and special variable $# The value
echo "Current Parameter: $1, Remaining $#."

# The flag variable is incremented by 1 operation
flag=`expr $flag + 1`
# Pass the value of $1 to a function or other operation
# Pass $1 to some bash function or do whatever
# Shift the positional parameter to the left by one
shift
# If the variable flag If it is greater than 5, break out of the loop
if [ $flag -gt 5 ]
then
break
fi
done

echo "================================================ ====================The end of the first while loop======================== ========================================="

# The condition for exiting the while loop is changed to the value of $1 not being empty;

while [ -n "$1" ]
do

# Print the value of special variable $1 and the value of special variable $#
echo "Current Parameter: $1, Remaining $#."

# Pass $1
to some bash function or do whatever

# Shift the positional parameter left by one
shift

done
echo "================================================ =====================End of the second while loop======================== =========================================="

Two: Script Test

[root@www standandinout]# ./shiftreadparam.sh one two three four
Current Parameter: one, Remaining 4.
Current Parameter: two, Remaining 3.
Current Parameter: three, Remaining 2.
Current Parameter: four, Remaining 1.
====================================================================第一个while循环结束=================================================================
====================================================================第二个while循环结束=================================================================
[root@www standandinout]# ./shiftreadparam.sh one two three four five
Current Parameter: one, Remaining 5.
Current Parameter: two, Remaining 4.
Current Parameter: three, Remaining 3.
Current Parameter: four, Remaining 2.
Current Parameter: five, Remaining 1.
====================================================================第一个while循环结束=================================================================
====================================================================第二个while循环结束=================================================================
[root@www standandinout]# ./shiftreadparam.sh one two three four five six
Current Parameter: one, Remaining 6.
Current Parameter: two, Remaining 5.
Current Parameter: three, Remaining 4.
Current Parameter: four, Remaining 3.
Current Parameter: five, Remaining 2.
Current Parameter: six, Remaining 1.
================================================== ==================The end of the first while loop========================== =======================================
=========== ================================================== =======End of the second while loop====================================== ============================
[root@www standandinout]# ./shiftreadparam.sh one two three four five six seven eight
Current Parameter : one, Remaining 8.
Current Parameter: two, Remaining 7.
Current Parameter: three, Remaining 6.
Current Parameter: four, Remaining 5.
Current Parameter: five, Remaining 4.
Current Parameter: six, Remaining 3.
====================================================================第一个while循环结束=================================================================
Current Parameter: seven, Remaining 2.
Current Parameter: eight, Remaining 1.
====================================================================第二个while循环结束=================================================================
[root@www standandinout]# ./shiftreadparam.sh one two three four five six seven eight ten
Current Parameter: one, Remaining 9.
Current Parameter: two, Remaining 8.
Current Parameter: three, Remaining 7.
Current Parameter: four, Remaining 6.
Current Parameter: five, Remaining 5.
Current Parameter: six, Remaining 4.
================================================== ==================The end of the first while loop========================== =======================================
Current Parameter: seven, Remaining 3.
Current Parameter: eight, Remaining 2.
Current Parameter: ten, Remaining 1.
===================================== ===============================End of the second while loop============== ================================================== ==

Lead to questions:

For example, if we change the shift command in the script to 5 and pass a series of parameters, if the passed parameters cannot be divisible by 5; if we pass 9 command line parameters, after the first execution of $1, the value of $1 becomes six, The value of $# becomes 2; after the first shift operation, no more shifts will be performed, and the value of $1 is not empty, and $# is not 0, so iteration continues indefinitely. ,To solve this problem, you can use the exit status of ,shift. Check whether the shift command is executed by adding $? after the shift command to see if the value is 0. If the value of $? is non-zero, then terminate the loop

Three: shift [5] combined with $? to exit the loop

[root@www standandinout]# cat shift5readparam.sh
#!/bin/bash -
#================================ ================================================== =================================
#
#
# FILE: shiftreadparam.sh
# USAGE: ./shiftreadparam.sh
# DESCRIPTION: Read positional parameters: Use shift [n] to read multiple positional parameters; it is more convenient to use case for a single command line parameter; but multiple command line parameters are not reasonable, use the command shift command to read one after another in the variable Get the command line parameters directly.
# shift is a built-in command in Bash. This command is used to shift the passed parameter variable to the left. Its syntax: shift [n]; n is a non-negative integer less than or equal to "$#". If 0, the positional parameter will not be changed;
# If not specified, it will be set to 1 by default. If n is greater than $#, the positional parameters will not change.
# If n is greater than $# or less than 0, the status code of this status will be greater than 0, otherwise it will be 0; # # #
OPTIONS
:
-------
# REQUIREMENTS: ---------
#
# BUGS: ------
# NOTES: --------
# AUTHOR: ---------YangGe (TOM) ,[email protected]
# ORGANIZATION:
# CREATED: 2023-8-24 09:11:20
# REVISION: --------
#
#
#
#
#
#====================================================================================================================

# If the number of command line parameters is not 0, continue the while loop, otherwise exit the while loop
[ $# -ne 0 ]
do

# Print the value of special variable $1 and the value of special variable $#
echo "Current Parameter: $1, Remaining $#."

# Pass the value of $1 to a function or other operation
# Pass $1 to some bash function or do whatever
# Shift the positional parameter to the left by one
shift 5
# If the return value of the previous command is not 0, execute if statement
if [ $? -ne 0 ]
then
# Terminate the execution of the loop
break

fi

done

echo "================================================ ====================The end of the first while loop======================== ========================================="

echo "==========================================Loop terminated=== ================================================== ==============================================="

Four: Test script command execution

[root@www standandinout]# ./shift5readparam.sh one two three four five six senven
Current Parameter: one, Remaining 7.
Current Parameter: six, Remaining 2.
=============== ================================================== ===End of first while loop========================================== ========================
========================== ===============Loop terminated================================ ================================================== ===================