Replacing string in linux using sed/awk based

Question

i want to replace this

#!/usr/bin/env bash

with this

   #!/bin/bash

i have tried two approaches

Approach 1

original_str="#!/usr/bin/env bash"
replace_str="#!/bin/bash"

sed s~${original_str}~${replace_str}~ filename

Approach 2

line=`grep -n "/usr/bin" filename`
awk NR==${line} {sub("#!/usr/bin/env bash"," #!/bin/bash")}

But both of them are not working.

Answer 1

You cannot use ! inside a double quotes in BASH otherwise history expansion will take place.

You can just do:

original_str='/usr/bin/env bash'
replace_str='/bin/bash'

sed "s~$original_str~$replace_str~" file
#!/bin/bash

Answer 2

Using escape characters :

    $ cat z.sh
    #!/usr/bin/env bash

    $ sed -i "s/\/usr\/bin\/env bash/\/bin\/bash/g" z.sh

    $ cat z.sh
    #!/bin/bash