Inserting text to a file with Sed within Bash Script

Question

I tried to insert a text to the first line of a file using sed. I do this inside a bash script.

But why it hangs at the line of sed execution?

#! /bin/bash

# Command to execute
# ./mybashcode.sh test.nbq

nbqfile=$1   
nbqbase=$(basename $nbqfile nbq)
taglistfiletemp="${nbqbase}taglist_temp"
taglistfile="${nbqbase}taglist"


./myccode $nbqfile | 
sort | 
uniq -c | 
awk '{print $2}' > $taglistfiletemp 

noftags=$(wc -l $taglistfiletemp | awk '{print $1}')
echo $noftags


# We want to append output of noftags
# to the first line of taglistfile

sed '1i\
$noftags' > $taglistfile

# why it hangs here
# the content of taglistfile is NIL

Answer 1

I'm not sure what you are trying to do with sed but it needs two inputs, the script (usually a search/replace) and the data you want to perform it on. If you only specify one it assumes it has got the regular expression and waits for data on stdin. As you haven't supplied anything on stdin it'll hang indefinitely.

In addition, you have '$noftags' rather than "$noftags". The prior will output $noftags and the latter the contents of the variable, as single quotes do not allow variable expansion.

Answer 2

Have I got something wrong here?
Or, all you want to do is insert some text at the start of another file?

# $NewInitialText
# $fileToInsertInto
echo $NewInitialText > temp.file.txt
cat $fileToInsertInto >> temp.file.txt
mv temp.file.txt $fileToInsertInto

Is that easier done than sed? -- _{Pun intended I guess.}

Answer 3

it hangs because you forget to supply sed with the input file.

....
...
sed -i.bak "1i $noftags" $taglistfile 
...