Is it possible to pass an argument from a shell script and pass it to a file.
This is what I am essentially trying to achieve:
My script:
#!/bin/bash -
input=$1
DIR=/home/user/
File=$DIR/test.txt
`cat $File` < $input
this is the test.txt:
select * from abc where date=$input;
I am pretty new to this stuff. please help if there's a correct approach to it.
You don't need to use cat but rather echo for this particular scenario.
echo "select * from abc where date='$input'" > test.txt
The double quotes will redirect and WRITE the echo along with the sentence expanded input variable to the text.txt variable.
If you want to append as opposed to write, use:
echo "select * from abc where date='$input'" >> test.txt
Related
#!/bin/sh
...
read var
#user enters: it doesn't work
...
echo 'Some text and $var' > myfile.txt
Expected output:
cat myfile.txt
#Some text and it doesn't work
Actual output:
cat myfile.txt
#Some text and $var
So how to echo the content into the file with the value of the $var variable?
use double quote instead of simple quote to make variable remplacement available
you can also remove your quotes to make it work but it's not recommanded
http://wiki.bash-hackers.org/syntax/quoting
if you want to insert $var to last line(=append the content $var to file), please use >>
should be:
echo "Some text and $var" >> myfile.txt
the > is to override the content, whereas >> is to append the content to a file
So I am creating a variable and I want to echo it with an addition to the end like so:
I have a file: Filename-08-10-2017.txt
I create a variable:
myvariable=Filename*.txt
When I echo that variable:
echo $myvariable
it outputs Filename-08-10-2017.txt
But I want to change the name to .zip
So I am trying to go:
echo $myvariable.zip and have it output Filename-08-10-2017.txt.zip
however it outputs:
Filename*.txt.zip
How do I go about having it output the way I want?
Thanks.
EDIT:
I kind of figured it out.
I saved a new variable as $($myvariable) which saved the output.
The file name comes from glob expansion. If you want to iterate all files by using glob expansion, you can :
myvariable=Filename*.txt
for f in $myvariable; do echo $f; done
If you want to "disable" the glob expansion, e.g. get literial Filename*.txt by echo $myvariable, you can either set -f or just wrap the variable by double quote: echo "$myvariable".
To maniuplate the text you can do something like:
for f in $myvariable; do echo $f"whatever_like_zip"; done
if you want to do some text substitution, you can
for ... echo ${f/%txt/zip} ; done
It will change all txt file name to zip.
Also if you want to rename the file, change the above echo... into
mv "$f" "yourNewNameHere"
Anyway by reading your question I'm not quite clear, what do you really want.
Yuo can use sed
try this
file="test.txt"
newext=$(echo "$file" | sed -e "s|txt|zip|g")
echo $newext
I want to print code into a file using cat <<EOF >>:
cat <<EOF >> brightup.sh
!/bin/bash
curr=`cat /sys/class/backlight/intel_backlight/actual_brightness`
if [ $curr -lt 4477 ]; then
curr=$((curr+406));
echo $curr > /sys/class/backlight/intel_backlight/brightness;
fi
EOF
but when I check the file output, I get this:
!/bin/bash
curr=1634
if [ -lt 4477 ]; then
curr=406;
echo > /sys/class/backlight/intel_backlight/brightness;
fi
I tried putting single quotes but the output also carries the single quotes with it. How can I avoid this issue?
You only need a minimal change; single-quote the here-document delimiter after <<.
cat <<'EOF' >> brightup.sh
or equivalently backslash-escape it:
cat <<\EOF >>brightup.sh
Without quoting, the here document will undergo variable substitution, backticks will be evaluated, etc, like you discovered.
If you need to expand some, but not all, values, you need to individually escape the ones you want to prevent.
cat <<EOF >>brightup.sh
#!/bin/sh
# Created on $(date # : <<-- this will be evaluated before cat;)
echo "\$HOME will not be evaluated because it is backslash-escaped"
EOF
will produce
#!/bin/sh
# Created on Fri Feb 16 11:00:18 UTC 2018
echo "$HOME will not be evaluated because it is backslash-escaped"
As suggested by #fedorqui, here is the relevant section from man bash:
Here Documents
This type of redirection instructs the shell to read input from the
current source until a line containing only delimiter (with no
trailing blanks) is seen. All of the lines read up to that point are
then used as the standard input for a command.
The format of here-documents is:
<<[-]word
here-document
delimiter
No parameter expansion, command substitution, arithmetic expansion,
or pathname expansion is performed on word. If any characters in word
are quoted, the delimiter is the result of quote removal on word, and
the lines in the here-document are not expanded. If word is
unquoted, all lines of the here-document are subjected to parameter
expansion, command substitution, and arithmetic expansion. In the
latter case, the character sequence \<newline> is ignored, and \
must be used to quote the characters \, $, and `.
This should work, I just tested it out and it worked as expected: no expansion, substitution, or what-have-you took place.
cat <<< '
#!/bin/bash
curr=`cat /sys/class/backlight/intel_backlight/actual_brightness`
if [ $curr -lt 4477 ]; then
curr=$((curr+406));
echo $curr > /sys/class/backlight/intel_backlight/brightness;
fi' > file # use overwrite mode so that you don't keep on appending the same script to that file over and over again, unless that's what you want.
Using the following also works.
cat <<< ' > file
... code ...'
Also, it's worth noting that when using heredocs, such as << EOF, substitution and variable expansion and the like takes place. So doing something like this:
cat << EOF > file
cd "$HOME"
echo "$PWD" # echo the current path
EOF
will always result in the expansion of the variables $HOME and $PWD. So if your home directory is /home/foobar and the current path is /home/foobar/bin, file will look like this:
cd "/home/foobar"
echo "/home/foobar/bin"
instead of the expected:
cd "$HOME"
echo "$PWD"
Or, using your EOF markers, you need to quote the initial marker so expansion won't be done:
#-----v---v------
cat <<'EOF' >> brightup.sh
#!/bin/bash
curr=`cat /sys/class/backlight/intel_backlight/actual_brightness`
if [ $curr -lt 4477 ]; then
curr=$((curr+406));
echo $curr > /sys/class/backlight/intel_backlight/brightness;
fi
EOF
IHTH
I know this is a two year old question, but this is a quick answer for those searching for a 'how to'.
If you don't want to have to put quotes around anything you can simply write a block of text to a file, and escape variables you want to export as text (for instance for use in a script) and not escape one's you want to export as the value of the variable.
#!/bin/bash
FILE_NAME="test.txt"
VAR_EXAMPLE="\"string\""
cat > ${FILE_NAME} << EOF
\${VAR_EXAMPLE}=${VAR_EXAMPLE} in ${FILE_NAME}
EOF
Will write '"${VAR_EXAMPLE}="string" in test.txt' into test.txt
This can also be used to output blocks of text to the console with the same rules by omitting the file name
#!/bin/bash
VAR_EXAMPLE="\"string\""
cat << EOF
\${VAR_EXAMPLE}=${VAR_EXAMPLE} to console
EOF
Will output '"${VAR_EXAMPLE}="string" to console'
cat with <<EOF>> will create or append the content to the existing file, won't overwrite. whereas cat with <<EOF> will create or overwrite the content.
cat test.txt
hello
cat <<EOF>> test.txt
> hi
> EOF
cat test.txt
hello
hi
cat <<EOF> test.txt
> haiiiii
> EOF
cat test.txt
haiiiii
I'm trying to write a pretty basic script in Linux shell but I'm still learning. Basically, everything is good to go except one part. I direct two outputs into the same file, e.g.:
echo `losetup -a` > partitionfile
echo "p1" >> partition final
Basically, I need to add the letter/number "p1" to the end of whatever is written in the file.
The problem is, it ends up being read (cat partitionfile) as:
/dev/loop0
p1
I need it on the same line to it reads out as:
/dev/loop0p1
There has to be a way to fix this, I just don't know it. Any help would be much appreciated!
Thanks!
I would go for:
echo "$(losetup -a)p1" > partitionfile
For an example, see the following transcript:
pax> echo "$(echo xyzzy_)p1"
xyzzy_p1
The xyzzy_ is the output of the inner echo command (which in your case would be losetup) and the outer echo command appends p1.
Hi Actually the correct option of echo to achieve this is "\c"
\c Keeps the cursor on the same line.
However you cannot use \c unless you have enabled it with
-e
Thus your code should be something like this ...
echo -e "`losetup -a` \c" > partitionfile
echo "p1" >> partition final
this will write in partitionfile as
< output of losetup -a > p1
everything on same line.
You can pass -n flag to the first echo statement to not print the trailing new line.
Ref: http://linux.die.net/man/1/echo
I'm trying to execute a command for each line coming from a cat command. I'm basing this on sample code I got from a vendor.
Here's the script:
for tbl in 'cat /tmp/tables'
do
echo $tbl
done
So I was expecting the output to be each line in the file. Instead I'm getting this:
cat
/tmp/tables
That's obviously not what I wanted.
I'm going to replace the echo with an actual command that interfaces with a database.
Any help in straightening this out would be greatly appreciated.
You are using the wrong type of quotes.
You need to use the back-quotes rather than the single quote to make the argument being a program running and piping out the content to the forloop.
for tbl in `cat /tmp/tables`
do
echo "$tbl"
done
Also for better readability (if you are using bash), you can write it as
for tbl in $(cat /tmp/tables)
do
echo "$tbl"
done
If your expectations are to get each line (The for-loops above will give you each word), then you may be better off using xargs, like this
cat /tmp/tables | xargs -L1 echo
or as a loop
cat /tmp/tables | while read line; do echo "$line"; done
The single quotes should be backticks:
for tbl in `cat /etc/tables`
Although, this will not get you output/input by line, but by word. To process line by line, you should try something like:
cat /etc/tables | while read line
echo $line
done
With while loop:
while read line
do
echo "$line"
done < "file"
while IFS= read -r tbl; do echo "$tbl" ; done < /etc/tables
read this.
You can do a lot of parsing in bash by redefining the IFS (Input Field Seperator), for example
IFS="\t\n" # You must use double quotes for escape sequences.
for tbl in `cat /tmp/tables`
do
echo "$tbl"
done