Shell Grammar Learning Chapter

Escape characters:

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When parsing text, double quotation marks parse the string, and single quotes keep literal meanings.

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echo $? This bash last process exit code

Double quotation marks are used to keep the literal value of all characters in quotation marks ( carriage return is no exception ), except in the following cases :

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Condition test: Exit code 0 indicates success, not 0 indicates failure

For shaping values,

-GT represents greater than or great

-ge represents greater than or equal to great equal

-eq represents equality equal

-lt means less than or little

-le means less than or equal to

Read Val means reading from standard input to Val

For string comparisons: Use =,== directly (recommended), or! =

Selectable $str1== $str 2, or "x$str1" = = "X$STR2" (recommended to prevent direct comparison when $str1 is empty, X is any character)

Single quotes are not allowed here, single quotation marks only literal meaning

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Shell Grammar Learning Chapter