kevinc@bearcat.lim.tek.com (Kevin Cosgrove 627-5212) (03/22/88)
Anyone know how to build *accessible* variable names on the fly in Bourne
shell? Below is a do nothing script which, I hope, demonstrates what I
want to do.
#!/bin/sh
onestring="A" # set the values of arbitrary strings
twostring="B"
threestring="C"
for string in one two three # loop thru string sets
do
var="${string}string" # var contains the name of the string
# I wish to get access to
echo "\$$var = ${var}" # how do I get the contents of the string
# "pointed to" by var?
echo
done
Yes, I know there are lots of other shells and/or languages which make
the above easy to do, but I'm trying to patch existing scripts, and this
would make it much easier to do.
Disclaimer: donning fire resistant suit now...
__________________________________________________________________________
Kevin Cosgrove Tektronix, Inc.
(503)-627-5212 PO Box 500, M/S 47-092
kevinc@bearcat.LIM.TEK.COM Beaverton, OR 97077
__________________________________________________________________________ron@topaz.rutgers.edu (Ron Natalie) (03/23/88)
Try eval...
onestring="A" # set the values of arbitrary strings
twostring="B"
threestring="C"
for string in one two three # loop thru string sets
do
var="${string}string" # var contains the name of the string
# I wish to get access to
echo \$$var=`eval echo \\$$var`
done
mtr@eagle.ukc.ac.uk (M.T.Russell) (03/24/88)
In article <12565@brl-adm.ARPA> kevinc@bearcat.lim.tek.com (Kevin Cosgrove 627-5212) writes: >Anyone know how to build *accessible* variable names on the fly in Bourne >shell? One method is to echo appropriate magic to a file, and then source that file. Thus the following Bourne shell fragment fred="hello world" varname=fred echo result=\$$varname > tmpfile . tmpfile sets the variable result to $fred, or "hello world" in this case. By the way, I find the "." command very useful in shell scripts. Arguably it's better than shell functions because you get named parameters - you can do things like question="Do you want to load all the software" default=yes . ask # ask is a neat script for asking questions if [ "$answer" = yes ]; then ... where the shell variables question and default are effectively parameters to the ask script, and answer is the return value. You have to be disciplined with variable names though, as all variables are of course global. Mark Russell mtr@ukc.ac.uk
alen@cogen.UUCP (Alen Shapiro) (03/24/88)
In article <12565@brl-adm.ARPA> kevinc@bearcat.lim.tek.com (Kevin Cosgrove 627-5212) writes: >Anyone know how to build *accessible* variable names on the fly in Bourne >shell? Below is a do nothing script which, I hope, demonstrates what I >want to do. > >#!/bin/sh >onestring="A" # set the values of arbitrary strings >twostring="B" >threestring="C" >for string in one two three # loop thru string sets >do > var="${string}string" # var contains the name of the string > # I wish to get access to > > echo "\$$var = ${var}" # how do I get the contents of the string > # "pointed to" by var? > echo >done > >Yes, I know there are lots of other shells and/or languages which make >the above easy to do, but I'm trying to patch existing scripts, and this >would make it much easier to do. Nice exercise - try this. BTW /bin/calendar is a GREAT crib sheet for such things #!/bin/sh onestring="A" twostring="B" threestring="C" for string in one two three do var="a=\$${string}string" eval $var echo ${string}string = $a done --alen the Lisa slayer (it's a long story) In te re st in g li ne fi ll er go es he re
alan@ecrcvax.UUCP (Alan P. Sexton) (03/24/88)
In article <12565@brl-adm.ARPA> kevinc@bearcat.lim.tek.com (Kevin Cosgrove 627-5212) writes: >Anyone know how to build *accessible* variable names on the fly in Bourne >shell? Below is a do nothing script which, I hope, demonstrates what I >want to do. > >#!/bin/sh >onestring="A" # set the values of arbitrary strings >twostring="B" >threestring="C" >for string in one two three # loop thru string sets >do > var="${string}string" # var contains the name of the string > # I wish to get access to > > echo "\$$var = ${var}" # how do I get the contents of the string > # "pointed to" by var? > echo >done Here is an example that I think will show how to do what you want. I wrote it a looooong time ago to learn how to do shell programming and kept it as a reference. I make no claim that it is a `good' example of a sh script - merely that it shows how to pretend that sh has dynamic array variables and the like. The script records a persons name, the number of hours of lectures and the number of hours of tutorials he has given. It is very stupid and it would be far easier to just edit a file to record the data. a script of a sample is included. I originally wrote this on a version 7 system (yes THAT long ago) and I just fixed it so that it works on a bsd4.3 system so that I could get the typescript. Alan Sexton ECRC, Arabellastr 17, alan@ecrcvax.UUCP 8000 Muenchen 81, West Germany mcvax!unido!ecrcvax!alan tel. (089) 92699164 #! /bin/sh # This is a shell archive, meaning: # 1. Remove everything above the #! /bin/sh line. # 2. Save the resulting text in a file. # 3. Execute the file with /bin/sh (not csh) to create the files: # paycheck # typescript # This archive created: Thu Mar 24 12:28:57 1988 export PATH; PATH=/bin:$PATH echo shar: extracting "'paycheck'" '(1874 characters)' if test -f 'paycheck' then echo shar: will not over-write existing file "'paycheck'" else sed 's/^X//' << \SHAR_EOF > 'paycheck' X#! /bin/sh XN=1 Xif test -f "$1" Xthen X exec <$1 X while read NAME$N LECTS$N TUT$N X do X eval echo $"NAME$N" \\\ $"LECTS$N" \\\ $"TUT$N" X N=`expr $N + 1` X done X exec 0<&2 Xfi XNUMBER=`expr $N - 1` Xwhile true Xdo X while true X do X echo -n "Name: " X if read name X then X N=1 X while eval test $N -le $NUMBER -a \"$"NAME$N"\" != \""$name"\" X do X N=`expr $N + 1` X done X if test $N -gt $NUMBER X then X echo -n "New Lecturer? : " X read ANS X until test "$ANS" = "y" -o "$ANS" = "n" X do X echo -n "New Lecturer [y/n]? : " X read ANS X done X if test "$ANS" = "y" X then X eval NAME$N=$name X eval LECTS$N=0 X eval TUT$N=0 X NUMBER=$N X else X break X fi X fi X echo Name \ Lects. \ Tuts. X eval echo $"NAME$N" \\\ $"LECTS$N" \\\ $"TUT$N" X echo -n "Number of Lectures ? : " X read LECTS$N X echo -n "Number of Tutorials ? : " X read TUT$N X echo Name \ Lects. \ Tuts. X eval echo $"NAME$N" \\\ $"LECTS$N" \\\ $"TUT$N" X fi X ANS= X echo -n "Finished ? : " X read ANS X until test "$ANS" = "y" -o "$ANS" = "n" X do X echo -n "Finished [y/n] ? : " X read ANS X done X if test "$ANS" = "n" X then X break X else X break 2 X fi X done Xdone XN=1 Xwhile test $N -le $NUMBER Xdo X eval echo $"NAME$N" \\\ $"LECTS$N" \\\ $"TUT$N" X N=`expr $N + 1` Xdone Xecho 'output file name (<EOT> to quit with no output) : ' Xread file || ( echo "no output" ; exit 1 ) Xexec >$file XN=1 Xwhile test $N -le $NUMBER Xdo X eval echo $"NAME$N"\\\ $"LECTS$N"\\\ $"TUT$N" X N=`expr $N + 1` Xdone SHAR_EOF if test 1874 -ne "`wc -c < 'paycheck'`" then echo shar: error transmitting "'paycheck'" '(should have been 1874 characters)' fi chmod +x 'paycheck' fi # end of overwriting check echo shar: extracting "'typescript'" '(1025 characters)' if test -f 'typescript' then echo shar: will not over-write existing file "'typescript'" else sed 's/^X//' << \SHAR_EOF > 'typescript' XScript started on Thu Mar 24 12:23:20 1988 X% paycheck XName: alan XNew Lecturer? : y XName Lects. Tuts. Xalan 0 0 XNumber of Lectures ? : 2 XNumber of Tutorials ? : 3 XName Lects. Tuts. Xalan 2 3 XFinished ? : n XName: john XNew Lecturer? : y XName Lects. Tuts. Xjohn 0 0 XNumber of Lectures ? : 3 XNumber of Tutorials ? : 4 XName Lects. Tuts. Xjohn 3 4 XFinished ? : y Xalan 2 3 Xjohn 3 4 Xoutput file name (<EOT> to quit with no output) : Xtst X% X% cat tst Xalan 2 3 Xjohn 3 4 X% paycheck tst Xalan 2 3 Xjohn 3 4 XName: john XName Lects. Tuts. Xjohn 3 4 XNumber of Lectures ? : 4 XNumber of Tutorials ? : 6 XName Lects. Tuts. Xjohn 4 6 XFinished ? : n XName: fred XNew Lecturer? : y XName Lects. Tuts. Xfred 0 0 XNumber of Lectures ? : 1 XNumber of Tutorials ? : 2 XName Lects. Tuts. Xfred 1 2 XFinished ? : y Xalan 2 3 Xjohn 4 6 Xfred 1 2 Xoutput file name (<EOT> to quit with no output) : Xtst X% cat tst Xalan 2 3 Xjohn 4 6 Xfred 1 2 X% ^D Xscript done on Thu Mar 24 12:26:07 1988 SHAR_EOF echo shar: 2 control characters may be missing from "'typescript'" if test 1025 -ne "`wc -c < 'typescript'`" then echo shar: error transmitting "'typescript'" '(should have been 1025 characters)' fi fi # end of overwriting check # End of shell archive exit 0 -- Alan Sexton ECRC, Arabellastr 17, alan@ecrcvax.UUCP 8000 Muenchen 81, West Germany mcvax!unido!ecrcvax!alan tel. (089) 92699164
gwyn@brl-smoke.ARPA (Doug Gwyn ) (03/25/88)
In article <12565@brl-adm.ARPA> kevinc@bearcat.lim.tek.com (Kevin Cosgrove 627-5212) writes: >Anyone know how to build *accessible* variable names on the fly in Bourne >shell? Try using the "exec" built-in; it's a lot simpler and more efficient than most of the other proposals.
erik@naggum.se (Erik Naggum) (03/27/88)
I thought this was obvious for the -wizards, so I sent
kevinc@bearcat.lim.tek.com a private reply.
The right thing to do is _eval_. No . or exec will do the job very fast.
var='$'${foo}bar
eval echo '$var = ' $var
The very purpose of eval is to reevaluate the command line. (That is,
first evaluate the arguments, then execute them, i.e. evaluate them once
more.)
To everyone of those who have proposed wierd solutions:
Go read "An introduction to the UNIX Shell" by S. R. Bourne.
(Sorry if this offends anyone, but negligence on the part of reading
manuals is what I consider the hallmark of the novice. Besides, I learn
more and more things from reading the same manuals over and over.)
Yours in hacking (nonpejorative meaning),
Erik Naggum
UUCP -- erik@naggum.uucp UNIX is not ``eunuchs'' --
ARPA -- enag@ifi.uio.no in fact it's rather potent
Snail -- Naggum Software; POB 1560 VIKA; OSLO 0118; NORWAY; +47-2-384-400