Bash Built-In Variables: Difference between revisions
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* [[bash Concepts#bash_Environment_Variables|bash Concepts]] | * [[bash Concepts#bash_Environment_Variables|bash Concepts]] | ||
=Overview= | |||
==Environment Variable Hierarchy== | |||
When a parent shell forks a new sub-shell, the sub-shell process has a copy of the parent's environment and no access to the parent process's environment whatsoever. When the shell sub-process terminates any changes made to its environment are lost. | |||
=Standard Environment Variables= | =Standard Environment Variables= |
Revision as of 00:59, 4 March 2016
External
- bash Internal Variables http://www.tldp.org/LDP/abs/html/internalvariables.html
Internal
Overview
Environment Variable Hierarchy
When a parent shell forks a new sub-shell, the sub-shell process has a copy of the parent's environment and no access to the parent process's environment whatsoever. When the shell sub-process terminates any changes made to its environment are lost.
Standard Environment Variables
IFS
IFS is the internal field separator. This variable determines how bash recognizes fields (word boundaries) when it interprets character strings. IFS defaults to whitespace (space, tab and newline). This is the proof:
echo "$IFS" | cat -vte ^I$ $
IFS can be changed.
- Note you must set IFS back to whitespace after setting it to something else, so the basic shell function work as expected. This is done as shown below: restoring the default IFS value.
Restoring the default IFS value
IFS="$(printf ' \t\n')"
IFS and for
for honors the value of IFS (default the space). If you set IFS to something else, for will use that as field separator while iterating over the list. For more details see for and IFS
Related: