Processing of user input parameters in shell script

shell The processing of user input parameters in the script

bash shell The script provides 3 Plant from User department How to get data :

Command line arguments ( Add the data after the command )

Command line options

Read input directly from the keyboard

1 Command line arguments

image shell The most basic way for scripts to pass data is to use Command line arguments .

Example :

./add.sh 10 20

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This example provides the script add.sh Passed two Command line arguments (10 and 20).

1.1 Read the command line arguments

bash shell There are some special variables in , go by the name of Positional arguments (positional parameter).

The standard number of position parameters is :

$0 It's the program name ;

$1 Is the first parameter ;

$2 It's the second parameter ;

By analogy , $9 Is the ninth parameter .

${10} It's the tenth parameter …

Look at a request Factorial (factorial) Example :

$ cat temp.sh

#!/bin/bash

factorial=1

for (( i=1; i<=$1; i++)); do

factorial=$[$factorial * $i]

done

echo "the factorial of $1 is $factorial"

$ ./temp.sh 4

the factorial of 4 is 24

If shell Scripts need to be used Command line arguments , But the script does not add Command line arguments , Something could go wrong , For example, in the above example , If you run without parameters, an error will be reported :

$ ./temp.sh

./temp.sh: line 3: ((: i<=: syntax error: operand expected (error token is "<=")

the factorial of is 1

Generally, we need to check Command line arguments , Modify the above example :

$ cat temp.sh

#!/bin/bash
#  Command line arguments 1  Whether the string length is  zero
if [ -z "$1" ]; then
    echo "usage: $0 number"
    exit 0
fi
factorial=1
for (( i=1; i<=$1; i++)); do
    factorial=$[$factorial * $i]
done
echo "the factorial of $1 is $factorial"

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$ ./temp.sh

usage: ./temp.sh numbe

bash shell Several special variables are also provided :

$# Carried by the script when it runs Number of command line arguments ;

$* Put the... Provided on the command line All the parameters treat as A word preservation ;

[email protected] Put the... Provided on the command line All the parameters treat as Multiple independent words preservation .

Example :

$ cat temp.sh

#!/bin/bash
echo "There wre $# parameters supplied."
count=1
for param in "$*"; do
    echo "\$*,  Parameters $count = $param"
    count=$[ $count + 1 ]
done
count=1
for param in "[email protected]"; do
    echo "\[email protected],  Parameters $count = $param"
    count=$[ $count +1 ]
done

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$ ./temp.sh miyan rosie abby

There wre 3 parameters supplied.

$*, Parameters 1 = miyan rosie abby

[email protected], Parameters 1 = miyan

[email protected], Parameters 2 = rosie

[email protected], Parameters 3 = abby

If you put "$*" Double quotation marks on "" Get rid of , $* Will output and "[email protected]" The same result .

1.2 shell parameter expansion

Here are two commonly used Parameter extension :

${variable_name:-value}: If variable_name The value of is empty , return value.

${variable_name:?msg}: If variable_name The value of is empty , return message Error and exit .

Example :

$ cat temp.sh

#!/bin/bash
name=${1:? user name cannot be empty}
password=${2:-$(uuidgen | tr '[:upper:]' '[:lower:]')}
echo "username: $name, passowrd: $password"

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$ ./temp.sh

./temp.sh: line 2: 1:  user name cannot be empty

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$ ./temp.sh miyan

username: miyan, passowrd: e2c7956c-cd6c-4761-a323-a6785587b8f9

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2 Command options

Options (option) It's following Dashes (dash -) The last single letter , It can change the behavior of commands .

Handle Options involves getopt and getopts command .

Here is a brief introduction , When you need it, come back and make it up .

3 Get user input

Even though Command line options and Parameters It's from User department An important way to get input , But sometimes scripts need to be more interactive .

For example, ask a question when the script is running , Wait for the person who runs the script to answer , bash shell This provides read command .

3.1 read command

read variable_name From standard input ( keyboard ) or In another file descriptor Accept input , After receiving the input , read Data will be stored in variables .

read Order sample :

$ cat temp.sh

#!/bin/bash
# -n, don't output the trailing newline.
echo -n "Enter you name: "
read name
echo "Hello $name"

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$ ./temp.sh

Enter you name: miyan

Hello miyan

read Yes 3 Common use Options -p, -s and -t:

read -p “prompt text” variable_name: -p here stands for the prompt. Here we read the data along with some hint text .

read -s variable_name: This option -s means secret or secure whatever is used to read the sensitive data.

read -t seconds variable_name: Set up timeout Time , Unit second , Timeout returns non 0 Exit status code .

When read When reading multiple variables , Multiple variables are separated by spaces :

$ cat temp.sh

#!/bin/bash
read -p "three names: " u1 u2 u3
echo "Hello $u1, $u2, $u3 !!!"

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$ ./temp.sh

three names: miyan rosie abby

Hello miyan, rosie, abby !!!

3.2 Read from file

read The command can read the data saved in the file . Every time you call read command , It will read a line of text . When there is no content in the file , read Will exit and return to non 0 Of Exit status code .

The problem is how to transmit the file data to read ?

The most common way is Use... For files cat command , Pass the result through The Conduit Direct to contain read Ordered while command .

Look at an example :

$ cat test.txt

Crazy waves

hotel california

nothing's gonna change my love for you

$ cat temp.sh

#!/bin/bash
count=1
cat test.txt | while read line; do
    echo "line $count: $line"
    count=$[ $count + 1 ]
done

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$ ./temp.sh
line 1:  Crazy waves 
line 2: hotel california
line 3: nothing's gonna change my love for you

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There is also an advanced way of writing , use Input redirection :

$ cat temp.sh
#!/bin/bash
count=1
while read line; do
    echo "line $count: $line"
    count=$[ $count + 1 ]
done < test.txt

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$ ./temp.sh
line 1:  Crazy waves 
line 2: hotel california
line 3: nothing's gonna change my love for you

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