Linux & shell tools
Shell and permissions questions are small but easy to get wrong under pressure: whether a chmod value actually grants the access you intend, why a new file inherits permissions you didn't expect, or whether an argument with special characters will be interpreted by the shell before your script sees it. This page covers permission calculators, shell argument escaping, capability mask decoding and POSIX command line parsing.
The chmod calculator converts between rwx symbols and octal modes and explains special bits like setuid and sticky, while the umask calculator shows how a given umask changes the default permissions of new files and directories side by side. Shell escape quotes arguments correctly for POSIX, Bash or PowerShell so they reach a program as literal text instead of being reinterpreted. Everything works on the values or strings you type in, with nothing uploaded anywhere.
5 tools
All Linux & Shell tools
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Command Line and PATH Parser
Parse POSIX command syntax, PATH order and environment keys
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Linux capability decoder
Decode Linux capability hex masks to readable names and bits
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Shell escape
Quote arguments for POSIX, Bash and PowerShell without shell interpretation
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Chmod calculator
Convert between rwx symbols and octal modes with special bit explanation
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umask calculator
Compare file and directory permissions affected by umask masks
Linux & Shell tools FAQ
umask subtracts permission bits from a process's default, so a umask of 022 removes write access for group and others from newly created files and directories. The umask calculator compares the resulting file and directory permissions for a given mask side by side, clearer than working it out from octal subtraction.
Quoting rules differ between POSIX shells, Bash and PowerShell, and getting them wrong lets the shell split or reinterpret the argument before your program ever sees it. Shell escape quotes a given argument correctly for the target shell so it arrives as one literal string.
755 grants the owner read, write and execute while group and others get read and execute only, typical for a directory or an executable script. 644 grants the owner read and write with group and others limited to read, the usual mode for a regular data file. The chmod calculator shows both as symbols and octal side by side.