I want to save a command to a file (for example I want to save the string "cat /etc/passwd" to a file) but I can't use the echo command.
How can I create and save string to a file directly without using echo command?
You can redirect cat to a file, type the text, and press Control-D when you're done, like this:
cat > file.txt
some text
some more text
^D
By ^D I mean to press Control-D at the end. The line must be empty.
It will not be part of the file, it is just to terminate the input.
Are you avoiding ECHO for security purposes (e.g. you're using a shared terminal and you don't want to leave trace in the shell history of what you've written inside your files) or you're just curious for an alternative method?
Simple alternative to echo:
As someone said, redirecting cat is probably the simpler way to go.
I'd suggest you to manually type your end-of-file, like this:
cat <<EOF > outputfile
> type here
> your
> text
> and finish it with
> EOF
Here's the string you're asking for, as an example:
cat <<EOF > myscript.sh
cat /etc/passwd
EOF
You probably don't want everyone to know you've peeked into that file, but if that's your purpose please notice that wrapping it inside an executable file won't make it more private, as that lines will be logged anyway...
Security - Avoiding history logs etc..
In modern shell, just try adding a space at the beginning of every command and use freely whatever you want.
BTW, my best hint is to avoid using that terminal at all, if you can. If you got two shells (another machine or even just another secure user in the same machine), I'd recommend you using netcat. See here: http://www.thegeekstuff.com/2012/04/nc-command-examples/?utm_source=feedburner
{ { command ls $(dirname $(which cat)) |
grep ^ca't$'; ls /etc/passwd; } |
tr \\n ' '; printf '\n'; } > output-file
But it's probably a lot simpler to just do : printf 'cat /etc/passwd\n'
To be clear, this is a tongue-in-cheek solution. The initial command is an extraordinarily convoluted way to get what you want, and this is intended to be a humorous answer. Perhaps instructive to understand.
I am not sure I understood you correctly but
cat /etc/passwd > target.file
use the > operator to write it to file without echoing
If you need to use it, inside a program :
cat <<EOF >file.txt
some text
some more text
EOF
I would imagine that you are probably trying to print the content of a string to a file, hence you mentioned echo.
You are avoiding this:
echo "cat /etc/passwd" > target.file
You can use a here string combined with cat.
cat > target.file <<< "cat /etc/passwd"
Now the file target.file will contain a string cat /etc/passwd.
$ cat target.file
cat /etc/passwd
$
To create string:
var1=your command
to save a file or variable in a file without echo use:
cat $FILE/VAR1 > /new/file/path
Related
I remember doing magic with vi by "programming" it with input commands but I don't remember exactly how.
My sepcial request are:
launch vi in a script with command to be executed.
do an insert in one file.
search for a string in the file.
use $VARIABLE in the vi command line to replace something in the command.
finish with :wq.
I my memory, I sent the command exactly like in vi and the ESC key was emulate by '[' or something near.
I used this command into script to edit and change files.
I'm going to see the -c option but for now I cannot use $VARIABLE and insert was impossible (with 'i' or 'o').
#!/bin/sh
#
cp ../data/* .
# Retrieve filename.
MODNAME=$(pwd | awk -F'-' '{ print $2 }')
mv minimod.c $MODNAME.c
# Edit and change filename into the file (from mimimod to the content of $VARIABLE).
vi $MODENAME.c -c ":1,$s/minimod/$MODNAME/" -c ':wq!'
This example is not functionning (it seems the $VARIABLE is not good in -c command).
Could you help me remember memory ;) ?
Thanks a lot.
Joe.
You should not use vi for non-interactive editing. There's already another tool for that, it's called sed or stream editor.
What you want to do is
sed -i 's/minimod/'$MODNAME'/g' $MODNAME.c
to replace your vi command.
Maybe you are looking for the ex command, that can be run non-interatively:
ex $MODENAME.c <<< "1,\$s/minimod/$MODNAME/
wq!
"
Or if you use an old shell that does not implement here strings:
ex $MODENAME.c << EOF
1,\$s/minimod/$MODNAME/
wq!
EOF
Or if you do not want to use here documents either:
echo "1,\$s/minimod/$MODNAME/" > cmds.txt
echo "wq!" >> cmds.txt
ex $MODENAME.c < cmds.txt
rm cmds.txt
One command per line in the standard input. Just remember not to write the leading :. Take a look at this page for a quick review of ex commands.
Granted, it would be better to use the proper tool for the job, that would be sed, as #IsaA answer suggests, or awk for more complex commands.
I am trying to cat a file.txt and loop it twice through the whole content and copy it to a new file file_new.txt. The bash command I am using is as follows:
for i in {1..3}; do cat file.txt > file_new.txt; done
The above command is just giving me the same file contents as file.txt. Hence file_new.txt is also of the same size (1 GB).
Basically, if file.txt is a 1GB file, then I want file_new.txt to be a 2GB file, double the contents of file.txt. Please, can someone help here? Thank you.
Simply apply the redirection to the for loop as a whole:
for i in {1..3}; do cat file.txt; done > file_new.txt
The advantage of this over using >> (aside from not having to open and close the file multiple times) is that you needn't ensure that a preexisting output file is truncated first.
Note that the generalization of this approach is to use a group command ({ ...; ...; }) to apply redirections to multiple commands; e.g.:
$ { echo hi; echo there; } > out.txt; cat out.txt
hi
there
Given that whole files are being output, the cost of invoking cat for each repetition will probably not matter that much, but here's a robust way to invoke cat only once:[1]
# Create an array of repetitions of filename 'file' as needed.
files=(); for ((i=0; i<3; ++i)); do files[i]='file'; done
# Pass all repetitions *at once* as arguments to `cat`.
cat "${files[#]}" > file_new.txt
[1] Note that, hypothetically, you could run into your platform's command-line length limit, as reported by getconf ARG_MAX - given that on Linux that limit is 2,097,152 bytes (2MB) that's not likely, though.
You could use the append operator, >>, instead of >. Then adjust your loop count as needed to get the output size desired.
You should adjust your code so it is as follows:
for i in {1..3}; do cat file.txt >> file_new.txt; done
The >> operator appends data to a file rather than writing over it (>)
if file.txt is a 1GB file,
cat file.txt > file_new.txt
cat file.txt >> file_new.txt
The > operator will create file_new.txt(1GB),
The >> operator will append file_new.txt(2GB).
for i in {1..3}; do cat file.txt >> file_new.txt; done
This command will make file_new.txt(3GB),because for i in {1..3} will run three times.
As others have mentioned, you can use >> to append. But, you could also just invoke cat once and have it read the file 3 times. For instance:
n=3; cat $( yes file.txt | sed ${n}q ) > file_new.txt
Note that this solution exhibits a common anti-pattern and fails to properly quote the arguments, which will cause issues if the filename contains whitespace. See mklement's solution for a more robust solution.
I want to ask if is possible to combine linux command and <
sendmail -S "lalalal" -f "dailaakak" -au "kakakak" <<EOF
>lalal:lalal
>opp:ttt
>ggg:zzz
EOF
I want to have something like that sendmail -S "lalalal" -f "dailaakak" -au "kakakak" <<EOF; lalal:lalal; opp:ttt; ggg:zzz; EOF
I need to use that not in bash script
If it has to be in one line without newlines use that:
echo -e "lalal:lalal\nopp:ttt\nggg:zzz" | sendmail -S "lalalal" -f "dailaakak" -au "kakakak"
echo -n interpretes escapes characters such as \n as a newline.
If you are asking whether you can use the << EOF in an interactive shell then the answer is yes, you can.
Note this functionality is called here document and that there can be any word instead of EOF. For example:
$ cat - << someword
> Here you
> can
> write text with as many
> newlines as you want.
> someword
Here you
can
write text with as many
newlines as you want.
(cat - prints whatever it receives on stdin)
For more information on here documents you can read for example this: http://tldp.org/LDP/abs/html/here-docs.html
I have tried and succeeded but it's messy. EOF simply does not like to accept substituted new lines for some reason so it needs to be put in another format. Now I'm sure this could be achieved with an expect script one one line but the below is what I have made and works.
echo "ssh localhost `printf "<< EOF\necho "Working!" >> /tmp/myfile \nEOF\n"`" > file.sh; chmod770 file.sh; ./file.sh
printf "<< EOF\necho Test! >> /tmp/myfile \nEOF\n" | xargs ssh localhost
Please ensure chmod file permissions are suitable for your own work case! Putting it into an environment variable instead of a file is also likely to work.
Normally when one wants to look at specific output lines from running something, one can do something like:
./a.out | grep IHaveThisString
but what if IHaveThisString is something which changes every time so you need to first run it, watch the output to catch what IHaveThisString is on that particular run, and then grep it out? I can just dump to file and later grep but is it possible to do something like background it and then bring it to foreground and bringing it back but now piped to some grep? Something akin to:
./a.out
Ctrl-Z
fg | grep NowIKnowThisString
just wondering..
No, it is only in your screen buffer if you didn't save it in some other way.
Short form: You can do this, but you need to know that you need to do it ahead-of-time; it's not something that can be put into place interactively after-the-fact.
Write your script to determine what the string is. We'd need a more detailed example of the output format to give a better example of usage, but here's one for the trivial case where the entire first line is the filter target:
run_my_command | { read string_to_filter_for; fgrep -e "$string_to_filter_for" }
Replace the read string_to_filter_for with as many commands as necessary to read enough input to determine what the target string is; this could be a loop if necessary.
For instance, let's say that the output contains the following:
Session id: foobar
and thereafter, you want to grep for lines containing foobar.
...then you can pipe through the following script:
re='Session id: (.*)'
while read; do
if [[ $REPLY =~ $re ]] ; then
target=${BASH_REMATCH[1]}
break
else
# if you want to print the preamble; leave this out otherwise
printf '%s\n' "$REPLY"
fi
done
[[ $target ]] && grep -F -e "$target"
If you want to manually specify the filter target, this can be done by having the loop check for a file being created with filter contents, and using that when starting up grep afterwards.
That is a little bit strange what you need, but you can do it tis way:
you must go into script session first;
then you use shell how usually;
then you start and interrupt you program;
then run grep over typescript file.
Example:
$ script
$ ./a.out
Ctrl-Z
$ fg
$ grep NowIKnowThisString typescript
You could use a stream editor such as sed instead of grep. Here's an example of what I mean:
$ cat list
Name to look for: Mike
Dora 1
John 2
Mike 3
Helen 4
Here we find the name to look for in the fist line and want to grep for it. Now piping the command to sed:
$ cat list | sed -ne '1{s/Name to look for: //;h}' \
> -e ':r;n;G;/^.*\(.\+\).*\n\1$/P;s/\n.*//;br'
Mike 3
Note: sed itself can take file as a parameter, but you're not working with text files, so that's how you'd use it.
Of course, you'd need to modify the command for your case.
I'm looking for a little shell script that will take anything piped into it, and dump it to a file.. for email debugging purposes. Any ideas?
The unix command tee does this.
man tee
cat > FILENAME
You're not alone in needing something similar... in fact, someone wanted that functionality decades ago and developed tee :-)
Of course, you can redirect stdout directly to a file in any shell using the > character:
echo "hello, world!" > the-file.txt
The standard unix tool tee can do this. It copies input to output, while also logging it to a file.
Use Procmail. Procmail is your friend. Procmail is made for this sort of thing.
Use <<command>> | tee <<file>> for piping a command <<command>> into a file <<file>>.
This will also show the output.
If you want to analyze it in the script:
while /bin/true; do
read LINE
echo $LINE > $OUTPUT
done
But you can simply use cat. If cat gets something on the stdin, it will echo it to the stdout, so you'll have to pipe it to cat >$OUTPUT. These will do the same. The second works for binary data also.
If you want a shell script, try this:
#!/bin/sh
exec cat >/path/to/file
If exim or sendmail is what's writing into the pipe, then procmail is a good answer because it'll give you file locking/serialization and you can put it all in the same file.
If you just want to write into a file, then
- tee > /tmp/log.$$
or
- cat > /tmp/log.$$
might be good enough.
Huh? I guess, I don't get the question?
Can't you just end your pipe into a >> ~file
For example
echo "Foobar" >> /home/mo/dumpfile
will append Foobar to the dumpfile (and create dumpfile if necessary). No need for a shell script... Is that what you were looking for?
if you don't care about outputting the result
cat - > filename
or
cat > filename