I'm using the bourne shell in UNIX, and am running into the following problem:
#!/bin/sh
while read line
do
echo $line
if [ $x = "true" ]
then
echo "something"
read choice
echo $choice
else
echo "something"
fi
done <file.txt
The problem I have here is that UNIX will not wait for user input in the read command - it just plows on through instead of waiting for what the user types in. How can I make unix wait for user input?
It is because you are asking the program to read from the file file.txt:
done <file.txt
Also looks like you have a typo here:
if [ $x = "true" ]
^^
which should be "$line". Also note the ", without them your program will break if the word read from the file has a space in it.
The redirection of standard input by the <file.txt at the end of while ... done <file.txt affects the whole while loop, including the read choice as well as the read line. It's not just failing to stop - it's consuming a line of your input file too.
Here's one way to solve the problem...
You can save the original standard input by using the somewhat obscure (even by shell standards):
exec 3<&0
which opens file descriptor 3 to refer to the original file descriptor 0, which is the original standard input. (File descriptors 0, 1 and 2 are standard input, output and error respectively.) And then you can redirect just the input of read choice to come from file descriptor 3 by doing read choice <&3.
Complete working script (I wasn't sure where x was supposed to come from, so I just bodged it to make it work):
#!/bin/sh
x=true # to make the example work
exec 3<&0
while read line
do
echo $line
if [ $x = "true" ]
then
echo "something"
read choice <&3
else
echo "something"
fi
done <file.txt
I don't do much shell scripting, but i think 'read choice' should be 'read $choice'
Related
I am creating a KSH interface script that will call other scripts based on the users input. The other scripts are Encrypt and Decrypt. Each one of these scripts receive parameters. I have seen someone execute a script before using "-" + first letter of a script name before. How do I do this for my script? So for example if my script is called menu and the user typed in : menu -e *UserID Filename.txt* the script would run and the encrypt script would be executed along with the associated parameters. So far my script takes in the encrypt/decrypt script option as a parameter. Here is my script:
#!/bin/ksh
#I want this parameter to become an
action=$1
if [ $1 = "" ]
then
print_message "Parameters not satisfied"
exit 1
fi
#check for action commands
if [ $1 = "encrypt" ]
then
dest=$2
fileName=$3
./Escript $dest $fileName
elif [ $1 = "decrypt" ]
then
outputF=$2
encryptedF=$3
./Dscript $outputF $encryptedF
else
print "Parameters not satisfied. Please enter encrypt or decrypt plus-n arguments"
fi
Thanks for the help!
There isn't any kind of automatic way to turn a parameter into another script to run; what you're doing is pretty much how you would do it. Check the parameter, and based on the contents, run the two different scripts.
You can structure it somewhat more nicely using case, and you can pass the later parameters directly through to the other script using "$#", with a shift to strip off the first parameter. Something like:
[ $# -ge 1 ] || (echo "Not enough parameters"; exit 1)
command=$1
shift
case $command in
-e|--encrypt) ./escript "$#" ;;
-d|--decrypt) ./dscript "$#" ;;
*) echo "Unknown option $command"; exit 1 ;;
esac
This also demonstrates how you can implement both short and long options, by providing two different strings to match against in a single case statement (-e and --encrypt), in case that's what you were asking about. You can also use globs, like -e*) to allow any option starting with -e such as -e, -encrypt, -elephant, though this may not be what you're looking for.
I need to get exactly one character from console and not print it.
I've tried to use read -en 1 as I did using bash. But this doesn't work at all.
And vared doesn't seem to have such option.
How to read 1 symbol in zsh? (I'm using zsh v.4.3.11 and v.5.0.2)
read -sk
From the documentation:
-s
Don’t echo back characters if reading from the terminal. Currently does not work with the -q option.
-k [ num ]
Read only one (or num) characters. All are assigned to the first name, without word splitting. This flag is ignored when -q is present. Input is read from the terminal unless one of -u or -p is present. This option may also be used within zle widgets.
Note that despite the mnemonic ‘key’ this option does read full characters, which may consist of multiple bytes if the option MULTIBYTE is set.
If you want your script to be a bit more portable you can do something like this:
y=$(bash -c "read -n 1 c; echo \$c")
read reads from the terminal by default:
% date | read -sk1 "?Enter one char: "; echo $REPLY
Enter one char: X
Note above:
The output of date is discarded
The X is printed by the echo, not when the user enters it.
To read from a pipeline, use file descriptor 0:
% echo foobar | read -rk1 -u0; echo $REPLY
f
% echo $ZSH_VERSION
5.5.1
Try something like
read line
c=`echo $line | cut -c1`
echo $c
I have a filewatcher.txt file . i want to include a piece of code in an existing unix script(final) that will ask user for input(Y/N) to check whether the file has been renamed(*filewatcher.txt e.g.SAV_filewatcher.txt or xyz_filewatcher.txt ) or the original name(filewatcher.txt) exists.
If the file watcher has not been renamed the existing code(final) will exit.
I'm not positive I understand what you're looking to do, but here are a few basic scripting tips:
if [ -f "filewatcher.txt" ]; then
echo "file has not been renamed"
fi
echo "Please give me some input"
read var
echo "Your input was $var"
I do not want:
$ cat file > dummy; $ cat header dummy > file
I want similar to the command below but to the beginning, not to the end:
$ cat header >> file
You can't append to the beginning of a file without rewriting the file. The first way you gave is the correct way to do this.
This is easy to do in sed if you can embed the header string directly in the command:
$ sed -i "1iheader1,header2,header3"
Or if you really want to read it from a file, you can do so with bash's help:
$ sed -i "1i$(<header)" file
BEWARE that "-i" overwrites the input file with the results. If you want sed to make a backup, change it to "-i.bak" or similar, and of course always test first with sample data in a temp directory to be sure you understand what's going to happen before you apply to your real data.
The whole dummy file thing is pretty annoying. Here's a 1-liner solution that I just tried out which seems to work.
echo "`cat header file`" > file
The ticks make the part inside quotes execute first so that it doesn't complain about the output file being an input file. It seems related to hhh's solution but a bit shorter. I suppose if the files are really large this might cause problems though because it seems like I've seen the shell complain about the ticks making commands too long before. Somewhere the part that is executed first must be stored in a buffer so that the original can be overwritten, but I'm not enough of an expert to know what/where that buffer would be or how large it could be.
You can't prepend to a file without reading all the contents of the file and writing a new file with your prepended text + contents of the file. Think of a file in Unix as a stream of bytes - it's easy to append to an end of a stream, but there is no easy operation to "rewind" the stream and write to it. Even a seek operation to the beginning of the file will overwrite the beginning of with any data you write.
One possibility is to use a here-document:
cat > "prependedfile" << ENDENDEND
prepended line(s)
`cat "file"`
ENDENDEND
There may be a memory limitation to this trick.
Thanks to right searchterm!
echo "include .headers.java\n$(cat fileObject.java )" > fileObject.java
Then with a file:
echo "$(cat .headers.java)\n\n$(cat fileObject.java )" > fileObject.java
if you want to pre-pend "header" to "file" why not append "file" to "Header"
cat file >> header
Below is a simple c-shell attempt to solve this problem. This "prepend.sh" script takes two parameters:
$1 - The file containing the pre-appending wording.
$2 - The original/target file to be modified.
#!/bin/csh
if (if ./tmp.txt) then
rm ./tmp.txt
endif
cat $1 > ./tmp.txt
cat $2 >> ./tmp.txt
mv $2 $2.bak
mv ./tmp.txt $2
I want my ksh script to have different behaviors depending on whether there is something incoming through stdin or not:
(1) cat file.txt | ./script.ksh (then do "cat <&0 >./tmp.dat" and process tmp.dat)
vs. (2) ./script.ksh (then process $1 which must be a readable regular file)
Checking for stdin to see if it is a terminal[ -t 0 ] is not helpful, because my script is called from an other script.
Doing "cat <&0 >./tmp.dat" to check tmp.dat's size hangs up waiting for an EOF from stdin if stdin is "empty" (2nd case).
How to just check if stdin is "empty" or not?!
EDIT: You are running on HP-UX
Tested [ -t 0 ] on HP-UX and it appears to be working for me. I have used the following setup:
/tmp/x.ksh:
#!/bin/ksh
/tmp/y.ksh
/tmp/y.ksh:
#!/bin/ksh
test -t 0 && echo "terminal!"
Running /tmp/x.ksh prints: terminal!
Could you confirm the above on your platform, and/or provide an alternate test setup more closely reflecting your situation? Is your script ultimately spawned by cron?
EDIT 2
If desperate, and if Perl is available, define:
stdin_ready() {
TIMEOUT=$1; shift
perl -e '
my $rin = "";
vec($rin,fileno(STDIN),1) = 1;
select($rout=$rin, undef, undef, '$TIMEOUT') < 1 && exit 1;
'
}
stdin_ready 1 || 'stdin not ready in 1 second, assuming terminal'
EDIT 3
Please note that the timeout may need to be significant if your input comes from sort, ssh etc. (all these programs can spawn and establish the pipe with your script seconds or minutes before producing any data over it.) Also, using a hefty timeout may dramatically penalize your script when there is nothing on the input to begin with (e.g. terminal.)
If potentially large timeouts are a problem, and if you can influence the way in which your script is called, then you may want to force the callers to explicitly instruct your program whether stdin should be used, via a custom option or in the standard GNU or tar manner (e.g. script [options [--]] FILE ..., where FILE can be a file name, a - to denote standard input, or a combination thereof, and your script would only read from standard input if - were passed in as a parameter.)
This strategy works for bash, and would likely work for ksh. Poll 'tty':
#!/bin/bash
set -a
if [ "$( tty )" == 'not a tty' ]
then
STDIN_DATA_PRESENT=1
else
STDIN_DATA_PRESENT=0
fi
if [ ${STDIN_DATA_PRESENT} -eq 1 ]
then
echo "Input was found."
else
echo "Input was not found."
fi
Why not solve this in a more traditional way, and use the command line argument to indicate that the data will be coming from stdin?
For an example, consider the difference between:
echo foo | cat -
and
echo foo > /tmp/test.txt
cat /tmp/test.txt