I have the following text:
Since the 1-93 fragment contains additional residues 84–93. The first hypen found in "1-93" is fine when I process the text but the second one, am not sure it is a hypen or another character that caused my problems, so I need to replace this "–" in text so at the end to get:
84 to 93 instead. Kindly how to do that.
You can always use a tool such as octal dump (od) or hexdump to confirm the ASCII code for a given character.
$ echo 'Since the 1-93 fragment contains additional residues 84–93.' | hexdump -C 00000000 53 69 6e 63 65 20 74 68 65 20 31 2d 39 33 20 66 |Since the 1-93 f| 00000010 72 61 67 6d 65 6e 74 20 63 6f 6e 74 61 69 6e 73 |ragment contains| 00000020 20 61 64 64 69 74 69 6f 6e 61 6c 0a 72 65 73 69 | additional.resi| 00000030 64 75 65 73 20 38 34 e2 80 93 39 33 2e 0a |dues 84...93..| 0000003e So the first - is ASCII code 2d, while the second – is not an ASCII code at all. So the dashes are clearly different. It's actually a UTF-8 character 0xe28093, an EN-DASH. (Thanks to @casey for clarifying this!)
To replace a character in a string such as this you can use either sed or put the string in a variable and do a search and replace on the string for this one character.
$ var='Since the 1-93 fragment contains additional\nresidues 84–93.' $ echo -e $var | sed 's/–/-/g' Since the 1-93 fragment contains additional residues 84-93. $ var='Since the 1-93 fragment contains additional\nresidues 84–93.' $ echo -e ${var/–/-} Since the 1-93 fragment contains additional residues 84-93. 
od was saying to me last night 8-). I've included your note in the A. You can use sed:
$ echo "Since the 1-93 fragment contains additional > residues 84–93." | sed 's/–/ to /g' Since the 1-93 fragment contains additional residues 84 to 93. To edit multiple files in-place, we use GNU sed, you can do:
sed -i 's/–/ to /g' ./*.txt 
printf %s – | recode ..dumptells you what character it is (U+2013, en dash here)