Difference between revisions of "Scripts on Linux"
Chris Tyler (talk | contribs) (New page: Linux kernels do not use file extensions such as .bat or .exe to identify the type of content in files (although some Linux applications may do so). Instead, a Linux system examines the fi...) |
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When an attempt is made to execute a file, the kernel will check the file [[Linux Permissions|permissions]]. If the effective user has permission to execute the file, it will be opened and the first few bytes examined for a 'magic number', which will identify the type of executable. If no magic number is found, and the file is a text file, it will be interpreted by the current shell (identified by the SHELL environment variable). | When an attempt is made to execute a file, the kernel will check the file [[Linux Permissions|permissions]]. If the effective user has permission to execute the file, it will be opened and the first few bytes examined for a 'magic number', which will identify the type of executable. If no magic number is found, and the file is a text file, it will be interpreted by the current shell (identified by the SHELL environment variable). | ||
| − | If the first two characters of the file are "#!" (which is considered a magic number), then the rest of the first line of the file is used as the absolute path and arguments for the interpreter. This is called a "shbang" line, from "#" (sharp) and "!" (bang). Therefore, using this as the first line of your script: | + | If the first two characters of the file are "#!" (which is considered a magic number), then the rest of the first line of the file is used as the absolute path and arguments for the interpreter. This is called a "shbang" line, from "#" (sharp) and "!" (bang). Therefore, using this as the first line of your [[BASH]] script: |
#!/bin/bash | #!/bin/bash | ||
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Will force the kernel to launch /bin/bash as the interpreter for the script. This ensures that bash will used even if the user prefers ksh, csh, or some other shell for their command-line work. | Will force the kernel to launch /bin/bash as the interpreter for the script. This ensures that bash will used even if the user prefers ksh, csh, or some other shell for their command-line work. | ||
| − | There are three requirements for a valid | + | There are three requirements for a valid [[BASH]] script: |
# The first line of the script must be <code>#!/bin/bash</code> | # The first line of the script must be <code>#!/bin/bash</code> | ||
| − | # The rest of the file must contain | + | # The rest of the file must contain [[BASH]] commands. |
# The file must be made executable (see [[Linux Permissions]]). | # The file must be made executable (see [[Linux Permissions]]). | ||
Revision as of 15:42, 15 September 2008
Linux kernels do not use file extensions such as .bat or .exe to identify the type of content in files (although some Linux applications may do so). Instead, a Linux system examines the file contents and permissions.
When an attempt is made to execute a file, the kernel will check the file permissions. If the effective user has permission to execute the file, it will be opened and the first few bytes examined for a 'magic number', which will identify the type of executable. If no magic number is found, and the file is a text file, it will be interpreted by the current shell (identified by the SHELL environment variable).
If the first two characters of the file are "#!" (which is considered a magic number), then the rest of the first line of the file is used as the absolute path and arguments for the interpreter. This is called a "shbang" line, from "#" (sharp) and "!" (bang). Therefore, using this as the first line of your BASH script:
#!/bin/bash
Will force the kernel to launch /bin/bash as the interpreter for the script. This ensures that bash will used even if the user prefers ksh, csh, or some other shell for their command-line work.
There are three requirements for a valid BASH script:
- The first line of the script must be
#!/bin/bash - The rest of the file must contain BASH commands.
- The file must be made executable (see Linux Permissions).
