The following few threads on this site and StackOverflow were helpful for understanding how IFS works: What is IFS in context of for looping? How to loop over the lines of a file Bash, read line b...

2016年7月20日 · The default value for IFS consists of whitespace characters (to be precise: space, tab and newline). Each character can be a word boundary. So, with the default value of IFS, the loop above will print: Word: foo:bar Word: baz Word: rab In other words, the shell thinks that whitespace is a word boundary. Now, try setting IFS=: before executing ...

2015年6月12日 · IFS is the Input Field Separator, which means the string read will be split based on the characters in IFS. On a command line, IFS is normally any whitespace characters, that's why the command line splits at spaces. Doing something like VAR=value command means "modify the environment of command so that VAR will have the value value".

2023年2月20日 · The default value of IFS is space, tab and newline, so if foo prints out two lines hello world and howdy then the loop body is executed with x=hello, then x=world and x=howdy. If IFS is explicitly changed to contain a newline only, then the loop is …

The IFS= read -r line sets the environment variable IFS (to an empty value) specifically for the execution of read. This is an instance of the general simple command syntax: a (possibly empty) sequence of variable assignments followed by a command name and its arguments (also, you can throw in redirections at any point).

2017年3月15日 · Consecutive separator characters that are whitespace are treated as a single separator, so the result of the expansion of cat${IFS}file.txt is two words: cat and file.txt. Non-whitespace separators are treated separately, with something like IFS=',.'; cat${IFS}file.txt, cat would receive two arguments: an empty argument and file.txt.

2017年10月10日 · In old versions of bash you had to quote variables after <<<.That was fixed in 4.4. In older versions, the variable would be split on IFS and the resulting words joined on space before being stored in the temporary file that makes up that <<< redirection.

Any character in IFS that is not IFS whitespace, along with any adjacent IFS whitespace characters, delimits a field. A sequence of IFS whitespace characters is also treated as a delimiter. It means that IFS whitespace (space, tab and newline) is …

2021年3月19日 · An alternative way of doing this, suggested by LL3 in comments (now deleted), relies on prefixing the unset command by :, a built-in utility that does nothing, effectively commenting out the unset, when it's not needed:

As Stephane points out below, the order of characters within IFS is significant when expanding "$*". From the bash man page: "$*" is equivalent to "$1c$2c...", where c is the first character of the value of the IFS variable. If IFS is unset, the parameters are separated by spaces. If IFS is null, the parameters are joined without intervening ...