Replacing a line in a file after grep command - macos

Question

I'm trying to replace a 0x1 to 0x0 in a file, I managed to get the line but I didn't manage to replace the string.
Here is the code:
grep -B 2 setSecure filePath | head -n 1
How can I proceed from here to change the string on the file? I'm using OS X, and I want to change the string only on this line.
Input File:
sometext
.line 344
const/4 v1, 0x1
iput v1, p0, Lnagra/nmp/sdk/NMPVideoView;->mCurrentState:I
const/4 v1, 0x1
invoke-virtual {v0, v1}, Landroid/view/SurfaceView;->setSecure(Z)V
.line 344
const/4 v1, 0x1
iput v1, p0, Lnagra/nmp/sdk/NMPVideoView;->mCurrentState:I
sometext
Output:
const/4 v1, 0x1
Please note there is many lines that start with "const/4 v1, 0x1" in the file.
I need to change only the "0x1" above the "invoke-virtual {v0, v1}, Landroid/view/SurfaceView;->setSecure(Z)V"

Answer 1

Could you please try following and let me know if this helps you.
awk '/const\/4 v1, 0x1/{prev=$0;$NF="0x0";val=$0;getline;print;getline;if($0 ~ /invoke-virtual {v0, v1}/){print val ORS $0} else {print prev};prev=val="";next} 1' Input_file
In case you need to save output into Input_file itself then append > temp_file && mv temp_file Input_file to above code too.

Answer 2

This is going to look a little ugly but is actually not terribly complicated. Using sed:
sed '1h; 1!H; $!d; x; s#\(const/4 v1, \)0x1\([^\n]*\n[^\n]*\n[^\n]*setSecure[^\n]*\n\)#\10x0\2#' filename
(pass -i to edit in-place after testing). This works by first reading the whole file into the hold buffer, then matching several lines at once:
1h # If we're processing the first line, write it to the hold buffer
1!H # if not, append it to the hold buffer
$!d # If we're not at the end of the file, we're done with this line here.
x # When we finally get here, we're at the end of the file, and the whole
# file is in the hold buffer. Swap hold buffer and pattern space, so the
# whole file is in the pattern space.
# Then: apply transformation. The regex is somewhat ugly because of all the \ns,
# but all that's really happening here is that we match const/4 v1, 0x1 followed
# by two lines of which the second contains "setSecure", and then replace the
# 0x1 with 0x0.
#
# To understand it, consider that \n[^\n]*\n matches newline followed by non-
# newline characters followed by another newline, which is exactly one line.
# Similarly, \n[^\n]*setSecure[^\n]*\n matches a line
s#\(const/4 v1, \)0x1\([^\n]*\n[^\n]*\n[^\n]*setSecure[^\n]*\n\)#\10x0\2#
Since you're using MacOS: MacOS by default uses BSD sed, which is limited in a number of ways. I think back in the day it had problems with \n in its code, so you may have to swap literal newlines in there for them. Although to be frank, if you're going to use sed under MacOS, it'd be least painful to just install GNU sed from homebrew.

Answer 3

You can't use grep for this task, grep only print and not modify the file.
You can use awk.
awk -v seen='setSecure' -v search='0x1' -v rplt='0x0' -v lign=1 '
NR<3 {
a[NR]=$0
next }
$0 ~ seen {
sub( search , rplt , a[lign] ) }
{
a[NR]=$0
print a[lign]
delete a[lign++] }
END {
for( i=lign ; i<=NR ; i++ )
print a[i] }
' input
With sed
sed '1N;N;/setSecure[^\n]*$/bA;P;D;:A;s/0x1/0x0/;P;D' input
sed '
1
N
# Always keep two lines in the pattern space
N
# get a third one
# and search for your word
# if find jump to A
/setSecure[^\n]*$/bA
# not find
# print the first line of the pattern space
P
# delete it and start a new cycle
D
:A
# the word is find
# do the replacement
s/0x1/0x0/
# print the first line of the pattern space
P
# delete it and start a new cycle
D
' input
If it's ok, you can add -i "" to replace the file

Answer 4

Using your already working command to find out the line number, the following sed command will replace all occurrences of 0x1 to 0x0, on lines starting with 'const/4', if it appears at least 2 lines before a line containing 'setSecure'
$ for LN in $(grep -n -B 2 setSecure filePath | grep 'const/4' | cut -d '-' -f 1 ) ; do sed -i ${LN}s/0x1/0x0/g filePath ; done
On Mac, following works :
$ for LN in $(grep -n -B 2 setSecure filePath | grep 'const/4' | cut -d '-' -f 1 ) ; do sed -i.bu ${LN}s/0x1/0x0/g filePath ; done