I would love to learn more about 'read' so to enhance my shell scripting abilities.
Usually when I have a thirst for knowledge for any program, I simply type:
man [program]
Then I learn how to work a program. I've been doing it this way for the past 15 years.
But a few days ago, I stumbled onto the most useless and unexpected man page (IMO) for a program called 'read'. It's a commonly used program for reading user input and a lot of shell scripts use it.
Here's it being used in one of my shell scripts.. It simply grabs a variable and outputs it, whilst allowing it to be edited by the end user:
read -e -p "HOSTip: " -i "${HOSTip}" HOSTip
This command took a lot of trawling about the web to find how to use it in this way. The man page was zero help.
Any help would be greatly appreciated in helping me figure out why a proper manual for using read doesn't appear to exist on my machine.
If your shell is bash, its builtin commands don't have individual man pages. Use help to see a list of builtins and help <command> to get help on an individual one.
$ help
GNU bash, version 5.1.4(1)-release (x86_64-pc-linux-gnu)
These shell commands are defined internally. Type `help' to see this list.
Type `help name' to find out more about the function `name'.
Use `info bash' to find out more about the shell in general.
Use `man -k' or `info' to find out more about commands not in this list.
A star (*) next to a name means that the command is disabled.
job_spec [&] history [-c] [-d offset] [n] or history -anrw [filename>
(( expression )) if COMMANDS; then COMMANDS; [ elif COMMANDS; then COMMA>
. filename [arguments] jobs [-lnprs] [jobspec ...] or jobs -x command [args]
: kill [-s sigspec | -n signum | -sigspec] pid | jobspec >
[ arg... ] let arg [arg ...]
[[ expression ]] local [option] name[=value] ...
alias [-p] [name[=value] ... ] logout [n]
bg [job_spec ...] mapfile [-d delim] [-n count] [-O origin] [-s count] [->
bind [-lpsvPSVX] [-m keymap] [-f filename] [-q name] [-u> popd [-n] [+N | -N]
break [n] printf [-v var] format [arguments]
builtin [shell-builtin [arg ...]] pushd [-n] [+N | -N | dir]
caller [expr] pwd [-LP]
case WORD in [PATTERN [| PATTERN]...) COMMANDS ;;]... es> read [-ers] [-a array] [-d delim] [-i text] [-n nchars]>
cd [-L|[-P [-e]] [-@]] [dir] readarray [-d delim] [-n count] [-O origin] [-s count] >
command [-pVv] command [arg ...] readonly [-aAf] [name[=value] ...] or readonly -p
compgen [-abcdefgjksuv] [-o option] [-A action] [-G glob> return [n]
complete [-abcdefgjksuv] [-pr] [-DEI] [-o option] [-A ac> select NAME [in WORDS ... ;] do COMMANDS; done
compopt [-o|+o option] [-DEI] [name ...] set [-abefhkmnptuvxBCHP] [-o option-name] [--] [arg ...>
continue [n] shift [n]
coproc [NAME] command [redirections] shopt [-pqsu] [-o] [optname ...]
declare [-aAfFgiIlnrtux] [-p] [name[=value] ...] source filename [arguments]
dirs [-clpv] [+N] [-N] suspend [-f]
disown [-h] [-ar] [jobspec ... | pid ...] test [expr]
echo [-neE] [arg ...] time [-p] pipeline
enable [-a] [-dnps] [-f filename] [name ...] times
eval [arg ...] trap [-lp] [[arg] signal_spec ...]
exec [-cl] [-a name] [command [argument ...]] [redirecti> true
exit [n] type [-afptP] name [name ...]
export [-fn] [name[=value] ...] or export -p typeset [-aAfFgiIlnrtux] [-p] name[=value] ...
false ulimit [-SHabcdefiklmnpqrstuvxPT] [limit]
fc [-e ename] [-lnr] [first] [last] or fc -s [pat=rep] [> umask [-p] [-S] [mode]
fg [job_spec] unalias [-a] name [name ...]
for NAME [in WORDS ... ] ; do COMMANDS; done unset [-f] [-v] [-n] [name ...]
for (( exp1; exp2; exp3 )); do COMMANDS; done until COMMANDS; do COMMANDS; done
function name { COMMANDS ; } or name () { COMMANDS ; } variables - Names and meanings of some shell variables
getopts optstring name [arg ...] wait [-fn] [-p var] [id ...]
hash [-lr] [-p pathname] [-dt] [name ...] while COMMANDS; do COMMANDS; done
help [-dms] [pattern ...] { COMMANDS ; }
$ help read
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
-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 within TIMEOUT seconds. The value of the
TMOUT variable is the default timeout. TIMEOUT may be a
fractional number. If TIMEOUT is 0, read returns
immediately, without trying to read any data, returning
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
(in which case it's greater than 128), a variable assignment error occurs,
or an invalid file descriptor is supplied as the argument to -u.
You can also find their documentation collected in man builtins or near the bottom of the bash man page under "Shell Builtin Commands".