CODEWITHSUNDEEP
bashsyntax
Buttle Butkus
Buttle Butkus

Reputation: 9486

Bash script, please explain this syntax

while read dir ev file; do
    # do stuff
done

The part I can't find an explanation for is the read dir ev part. I'm not familiar with Bash. I mainly do PHP and MySQL. Can anyone explain?

Thanks.

Upvotes: 1

Views: 341

Answers (1)

Amber
Amber

Reputation: 527488

The short version is, it takes a single line at a time from the input and assigns individual fields from it into variables.

read dir ev file would read lines one by one and expect each line to contain 3 items. It would then assign the first item into a variable named dir, the second into a variable named ev, and the third into a variable named file.

From the output of help read:

(Edit: more readable version here: http://ss64.com/bash/read.html)

read: read [-ers] [-a array] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout] [-u fd] [name ...]
    Read a line from the standard input and split it into fields.

    Reads a single line from the standard input, or from file descriptor FD
    if the -u option is supplied.  The line is split into fields as with word
    splitting, and the first word is assigned to the first NAME, the second
    word to the second NAME, and so on, with any leftover words assigned to
    the last NAME.  Only the characters found in $IFS are recognized as word
    delimiters.

    If no NAMEs are supplied, the line read is stored in the REPLY variable.

    Options:
      -a array  assign the words read to sequential indices of the array
                variable ARRAY, starting at zero
      -d delim  continue until the first character of DELIM is read, rather
                than newline
      -e                use Readline to obtain the line in an interactive shell
      -i text   Use TEXT as the initial text for Readline
      -n nchars return after reading NCHARS characters rather than waiting
                for a newline, but honor a delimiter if fewer than NCHARS
                characters are read before the delimiter
      -N nchars return only after reading exactly NCHARS characters, unless
                EOF is encountered or read times out, ignoring any delimiter
      -p prompt output the string PROMPT without a trailing newline before
                attempting to read
      -r                do not allow backslashes to escape any characters
      -s                do not echo input coming from a terminal
      -t timeout        time out and return failure if a complete line of input is
                not read withint TIMEOUT seconds.  The value of the TMOUT
                variable is the default timeout.  TIMEOUT may be a
                fractional number.  If TIMEOUT is 0, read returns success only
                if input is available on the specified file descriptor.  The
                exit status is greater than 128 if the timeout is exceeded
      -u fd             read from file descriptor FD instead of the standard input

    Exit Status:
    The return code is zero, unless end-of-file is encountered, read times out,
    or an invalid file descriptor is supplied as the argument to -u.

Upvotes: 3

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