flory@zaphod.UUCP (Trevor Flory) (10/16/85)
Hello All;
I'm trying to debug a csh script written by someone who
knew what he was doing I'm sure. Below is a fragment of
the script which I find rather difficult to understand:
...
alias readandset 'echo -n \!:1 ; set \!:2 = $< '
...
readandset "Choice? " chvar
...
if("$chvar" == "quit") ....
In particular I'd like to know what \!:1 or \!:2 means/does.
Please note that I know the basics of csh but I'm no whiz so
a full, step-by-step parse of how the above fragment is
interpreted would not be out of order. Thanks very much for
your help. Post or e-mail as you see fit.
--
Trevor K. Flory UUCP: ...!ihnp4{!alberta}!sask!zaphod!flory
Develcon Electronics Ltd. Saskatoon, Saskatchewan, CANADA
"... the play is the tragedy, `Man',
And its hero the Conqueror Worm."
Poe, c.1838flory@zaphod.UUCP (Trevor Flory) (10/17/85)
In article <366@zaphod.UUCP> flory@zaphod.UUCP (that's me) writes: >Hello All; > I'm trying to debug a csh script .... Thanks to all who answered my Csh question. Also thanks to all who scorched my buns off with RTFM flames. -- Trevor K. Flory UUCP: ...!ihnp4{!alberta}!sask!zaphod!flory Develcon Electronics Ltd. Saskatoon, Saskatchewan, CANADA "... the play is the tragedy, `Man', And its hero the Conqueror Worm." Poe, c.1838
pdg@ihdev.UUCP (P. D. Guthrie) (10/18/85)
In article <366@zaphod.UUCP> flory@zaphod.UUCP (Trevor Flory) writes: >Hello All; > I'm trying to debug a csh script written by someone who > knew what he was doing I'm sure. Below is a fragment of > the script which I find rather difficult to understand: > ... > alias readandset 'echo -n \!:1 ; set \!:2 = $< ' > ... > readandset "Choice? " chvar > ... > if("$chvar" == "quit") .... > > In particular I'd like to know what \!:1 or \!:2 means/does. > This notation simply replaces itself with the corresponding arguments in the original line, so it echos the first argument, and sets the second one to a line from stdin. Why doesn't ksh have something like this? I hate having to use fc and mess around with its output - and that's soooo inefficient! Paul Guthrie
avolio@decuac.UUCP (Frederick M. Avolio) (10/19/85)
In article <366@zaphod.UUCP>, flory@zaphod.UUCP (Trevor Flory) writes: > Hello All; > I'm trying to debug a csh script written by someone who > knew what he was doing I'm sure. Below is a fragment of > the script which I find rather difficult to understand: > ... > alias readandset 'echo -n \!:1 ; set \!:2 = $< ' > ... > readandset "Choice? " chvar > ... > if("$chvar" == "quit") .... > > In particular I'd like to know what \!:1 or \!:2 means/does. If you look at a command line, the first word is in position 0, the next in position 1, and so on. !:n (where n is a non-negative number) the csh replaces the string with the word in the nth position from the previous command. (!:1 is the first word. !22:3 is the 3rd word from command #22 in the history and so on....) Example -- % ls -ld t* drwx--x--x 16 avolio 1024 Oct 17 15:23 text -rw-r--r-- 1 avolio 0 Oct 19 10:10 todo % ls !:2 ls t* todo text: cust.support decnet.info decuac kermit mail paths products qpr training uac uig ultrix11 ultrix32 venix ----- % echo a b c a b c % echo !:3 echo c c % And so on..... Fred.
itkin@luke.UUCP (Steven List) (10/20/85)
In article <366@zaphod.UUCP> you write: > alias readandset 'echo -n \!:1 ; set \!:2 = $< ' > ... > readandset "Choice? " chvar > ... > if("$chvar" == "quit") .... > > In particular I'd like to know what \!:1 or \!:2 means/does. Aliases use current line history replacement. \!:n means "replace with word n of the current command line", where 0 is the first word (usually the command itself). If readandset were to be written as a Bourne shell script, it would be as follows: prompt=$1 echo "$1\c" < /dev/tty > /dev/tty read X echo X and used as chvar=`readandset "Choice? "` thus storing the user's input into variable chvar. The use of "$<" in the alias is the equivalent of "read chvar" in Bourne shell or the alternate "set chvar = `line`" in C shell (ours does not support $<). Thus, readandset can be define is pseudocode as print the second word of this command as a prompt without a following newline store the response typed in in the variable named as the second argument (word 2, third object) The use of \!:n, where n can be any number, * (for all), or $ (for last), is a very powerful means of defining macros in the C shell. I use them all over the place very effectively (also refer to various means of implementing popd, pushd directory change macros). -- *** * Steven List @ Benetics Corporation, Mt. View, CA * Just part of the stock at "Uncle Bene's Farm" * {cdp,greipa,idi,oliveb,plx,sun,tolerant}!bene!luke!itkin ***
tweten@AMES-NAS.ARPA (10/24/85)
From: pdg@ihdev.UUCP (P. D. Guthrie)
> alias readandset 'echo -n \!:1 ; set \!:2 = $< '
Why doesn't ksh have something like this? I hate having to use
fc and mess around with its output - and that's soooo inefficient!
I'm not a ksher, so I can't answer directly, but System V.2 sh has just the
thing, shell functions:
readandset () { echo "$1\c"; read $2; }
To my eye, at least, it even looks better!