Input Field Separators
For many command line interpreters (“shell”) of Unix operating systems, the input field separators variable (abbreviated IFS, and often referred to as internal field separators) refers to a variable which defines the character or characters used to separate a pattern into tokens for some operations. The value of , typically includes the space, tab, and the newline by default. These whitespace characters can be visualized by printing with commands like codice_1, codice_2 or codice_3 (the latter two commands being only available in some shells and on some systems). From the Bash man page: The shell treats each character  of as a delimiter, and splits the results of the other expansions into words on these characters. If is unset, or its value is exactly , the default, then sequences of , , and at the beginning and end of the results of the previous expansions are ignored, and any sequence of characters not at the beginning or end serves to delimit words. If has a value other than the default, then sequences of the whitespace characters and are ignored at the beginning and end of the word, as long as the whitespace character is in the value of (an whitespace character). Any  character in that is not whitespace, along with any adjacent whitespace characters, delimits a field. A sequence of whitespace characters is also treated as a delimiter. If the value of is null, no word splitting occurs. IFS abbreviation. According to the Open Group Base Specifications, IFS is an abbreviation for "input field separators". A newer version of this specification mentions that "this name is misleading as the IFS characters are actually used as field terminators." However, IFS is often referred to as "internal field separators" on the internet. Exploits. IFS was usable as an exploit in some versions of Unix . A program with root permissions could be fooled into executing user-supplied code if it ran (for instance) codice_4 and was called with set to , in which case it would run the program "" (in the current directory and thus writable by the user) with root permissions. This has been fixed by making the shells not inherit the IFS variable.