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The test command in Unix evaluates the expression parameter. In most recent shell implementations, it is a shell builtin, even though the external version still exists.In the second form of the command, the [ ] (brackets) must be surrounded by blank spaces (this is because [is a program and POSIX compatible shells require a space between the program name and its arguments).
Shellshock, also known as Bashdoor, [1] is a family of security bugs [2] in the Unix Bash shell, the first of which was disclosed on 24 September 2014.Shellshock could enable an attacker to cause Bash to execute arbitrary commands and gain unauthorized access [3] to many Internet-facing services, such as web servers, that use Bash to process requests.
The old Unix lint program is an early example. For debugging electronic hardware (e.g., computer hardware ) as well as low-level software (e.g., BIOSes , device drivers ) and firmware , instruments such as oscilloscopes , logic analyzers , or in-circuit emulators (ICEs) are often used, alone or in combination.
Bash executes these files as part of its standard initialization, but other startup files can read them in a different order than the documented Bash startup sequence. The default content of the root user's files may also have issues, as well as the skeleton files the system provides to new user accounts upon setup.
JP Software command-line processors provide user-configurable colorization of file and directory names in directory listings based on their file extension and/or attributes through an optionally defined %COLORDIR% environment variable. For the Unix/Linux shells, this is a feature of the ls command and the terminal.
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>& file means both stdout and stderr will be written to file, overwriting it if it exists, and creating it if it doesn't. >> file means stdout will be appended at the end of file. >>& file means both stdout and stderr will be appended at the end of file. < file means stdin will be read from file. << string is a here document.
A similar problem exists for the POSIX shell, since POSIX only required its name to be sh, but did not mandate a path. A common value is /bin/sh, but some systems such as Solaris have the POSIX-compatible shell at /usr/xpg4/bin/sh. [13] In many Linux systems, /bin/sh is a hard or symbolic link to /bin/bash, the Bourne Again shell (BASH).