對這文章發表回應
發表限制: 非會員 可以發表
發表者： 冷日 發表時間： 2016/8/16 2:19:05
Linux/UNIX: Find Out If File Exists With Conditional Expressions
by VIVEK GITE on FEBRUARY 16, 2006 last updated JANUARY 25, 2016
With the help of BASH shell and IF command, it is possible to find out if file exists or not on the filesystem. A conditional expressions (also know as “evaluating expressions”) can be used by [[ compound command and the test ([) builtin commands to test file attributes and perform string and arithmetic comparisons.
Syntax
The general syntax is:
OR
OR
Where parameter can be any one of the following:
Please note that the [[ works only in Bash, Zsh and the Korn shell, and is more powerful; [ and test are available in POSIX shells. Let us see some examples.
Find out if file /etc/passwd file exist or not
Type the following commands:
[[ example
Type the following commands:
Find out if directory /var/logs exist or not
Type the following commands:
[[ example
Are two files are the same?
Use the -ef primitive with the [[ new test command:
Shell script example
You can use conditional expressions in a shell script:
You can use this technique to verify that backup directory or backup source directory exits or not in shell scripts. See example script for more information.
原文出處：Linux/UNIX: Find Out If File Exists With Conditional Expressions
by VIVEK GITE on FEBRUARY 16, 2006 last updated JANUARY 25, 2016
With the help of BASH shell and IF command, it is possible to find out if file exists or not on the filesystem. A conditional expressions (also know as “evaluating expressions”) can be used by [[ compound command and the test ([) builtin commands to test file attributes and perform string and arithmetic comparisons.
Syntax
The general syntax is:
[ parameter FILE ]
OR
test parameter FILE
OR
[[ parameter FILE ]]
Where parameter can be any one of the following:
-e: Returns true value if file exists.
-f: Return true value if file exists and regular file.
-r: Return true value if file exists and is readable.
-w: Return true value if file exists and is writable.
-x: Return true value if file exists and is executable.
-d: Return true value if exists and is a directory.
Please note that the [[ works only in Bash, Zsh and the Korn shell, and is more powerful; [ and test are available in POSIX shells. Let us see some examples.
Find out if file /etc/passwd file exist or not
Type the following commands:
$ [ -f /etc/passwd ] && echo "File exist" || echo "File does not exist"
$ [ -f /tmp/fileonetwo ] && echo "File exist" || echo "File does not exist"
[[ example
Type the following commands:
$ [[ -f /etc/passwd ]] && echo "File exist" || echo "File does not exist"
$ [[ -f /tmp/fileonetwo ]] && echo "File exist" || echo "File does not exist"
Find out if directory /var/logs exist or not
Type the following commands:
$ [ -d /var/logs ] && echo "Directory exist" || echo "Directory does not exist"
$ [ -d /dumper/fack ] && echo "Directory exist" || echo "Directory does not exist"
[[ example
$ [[ -d /var/logs ]] && echo "Directory exist" || echo "Directory does not exist"
$ [[ -d /dumper/fake ]] && echo "Directory exist" || echo "Directory does not exist"
Are two files are the same?
Use the -ef primitive with the [[ new test command:
[[ /etc/resolv.conf -ef /etc/resolv.conf ]] && echo "Same files" || echo "Noop"
[[ /etc/resolv.conf -ef /etc/passwd ]] && echo "Same files" || echo "Noop"
Shell script example
You can use conditional expressions in a shell script:
#!/bin/bash
FILE="$1"
if [ -f "$FILE" ];
then
echo "File $FILE exist."
else
echo "File $FILE does not exist" >&2
fi
Save and execute the script:
$ chmod +x script.sh
$ ./script.sh /path/to/file
$ ./script.sh /etc/resolv.conf
You can use this technique to verify that backup directory or backup source directory exits or not in shell scripts. See example script for more information.
原文出處：Linux/UNIX: Find Out If File Exists With Conditional Expressions