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ar:tldr:2f5e2
The command "ar x ${filename-a}" is written in a shell scripting language and is used to extract files from an archive created with the "ar" command.
Here's what each part of the command means:
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"ar": This is a command-line utility in Unix-like operating systems used to create, modify, and extract files from archives.
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"x": This is an option of the "ar" command, which specifies that the files should be extracted from the archive.
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"${filename-a}": This is a variable in the shell scripting language. The variable "filename" is being used, and the "-a" part is a default value for the variable if it is undefined or empty. This means that if the variable "filename" is not set, the default value "-a" will be used.
So, the command "ar x ${filename-a}" essentially means to extract files from an archive using the "ar" command, with the filename being specified by the variable "filename" (or defaulting to "-a" if the variable is not set).