1tweak(1) Simon Tatham tweak(1)
2
6 tweak - efficient hex editor
7
9 tweak [-l | -f] [-e] [-w width] [-o offset] filename
10
12 tweak is a hex editor. It allows you to edit a file at very low level,
13 letting you see the full and exact binary contents of the file. It can
14 be useful for modifying binary files such as executables, editing disk
15 or CD images, debugging programs that generate binary file formats
16 incorrectly, and many other things.
17 Unlike simpler hex editors, tweak possesses a fully functional insert
19 mode. This is not useful when editing many of the types of file
20 described above, but can be useful in other situations. Also, an insert
21 mode makes it easy to use tweak to construct new files from scratch.
22 When you open a file in tweak, you can expect to see the screen con‐
24 tents looking something like this:
25 00000000 7F 45 4C 46 01 01 01 00 .ELF....
27 00000008 00 00 00 00 00 00 00 00 ........
28 00000010 02 00 03 00 01 00 00 00 ........
29 00000018 D0 8E 04 08 34 00 00 00 ....4...
30 00000020 2C EF 01 00 00 00 00 00 ,.......
31 The central column shows you the hexadecimal value of each byte in the
33 file you are editing. The column on the right shows the ASCII interpre‐
34 tation of those bytes, where applicable. In the example above, the
35 sequence 45 4C 46 on the first line translates into the ASCII upper-
36 case letters `ELF', but the subsequent sequence 01 01 01 00 does not
37 have any printable ASCII representation and so the right-hand column
38 simply prints dots.
39 The column on the left shows the position within the file of the start
41 of each row.
42 In fact, when you start tweak, you will usually see 16 bytes of the
44 file per row, not 8 as shown above. However, this is configurable if
45 your screen is narrower - or wider - than the usual 80 columns, or if
46 the file you are editing consists of fixed-size records of some other
47 size.
48 By default, tweak does not load its entire input file into memory.
50 Instead, it loads it lazily, reading from the file on disk when you
51 request a view of a part of the file it doesn't have stored. When you
52 modify the file, it stores your modifications in memory, but continues
53 to refer to the original disk file for the parts you have not touched.
54 This means you can edit extremely large files (for example, entire CD
55 images) without difficulty; opening such a file is instantaneous, mak‐
56 ing modifications causes tweak's memory usage to grow with the size of
57 the changes rather than the size of the whole file, and only when sav‐
58 ing the altered version will tweak have to read through the entire
59 input file to write the output.
60 However, this mode of operation has a disadvantage, which is that if
62 the input file is modified by another program while tweak is running,
63 tweak's internal data structures will not be sufficient to keep track,
64 and it is likely that the file written out will contain a mixture of
65 the old and new contents of the input file. Therefore, you can disable
66 this lazy loading if you need to; see the -e option below.
67
69 This section lists the command-line options supported by tweak.
70 -f Runs tweak in `fix' mode, i.e. with the insert function entirely
72 disabled. This might be useful if you are editing a file in
73 which the insert mode is of no use (executables, for example,
74 tend to have strong dependencies on precise file offsets which
75 make it almost impossible to insert data in one without render‐
76 ing it unusable) and you want to avoid turning it on by mistake.
77 -l Runs tweak in `look' mode. In this mode tweak does not allow you
79 to modify the data at all; it becomes simply a tool for examin‐
80 ing a file in detail.
81 -e Runs tweak in `eager' mode. In this mode tweak will read its
83 entire input file when starting up. This causes it to take up
84 more memory, but means that it has no dependency on the input
85 file remaining unmodified, and other programs can alter it if
86 they need to without causing trouble.
87 -w width
89 Specifies the number of bytes tweak will display per line. The
90 default is 16, which fits neatly in an 80-column screen.
91 -o offset
93 If this option is specified, tweak will ensure that the given
94 file offset occurs at the start of a line. For example, if you
95 loaded a file using the options -w 8 -o 0x13, you might see a
96 display a bit like this:
97 00000000 7F 45 4C .EL
99 00000003 46 01 01 01 00 00 00 00 F.......
100 0000000B 00 00 00 00 00 02 00 03 ........
101 00000013 00 01 00 00 00 D0 8E 04 ........
102 0000001B 08 34 00 00 00 2C EF 01 .4...,..
103 By putting only three bytes of the file on the very first line,
105 tweak has arranged that the file offset 0x13 (19 in decimal)
106 appears at the beginning of the fourth line.
107 You might use this option if you knew you were editing a file in
109 a particular format. For example, if your file contained a
110 53-byte header followed by a series of 22-byte records, you
111 might find it useful to specify the options -w 22 -o 53. This
112 would arrange that after the header, each individual record of
113 the file would appear on precisely one line of tweak's display.
114 -D If this option is specified, tweak will not attempt to load and
116 edit a file at all, but will simply produce its default .tweakrc
117 file on standard output. This is a useful way to give yourself a
118 starting point if you want to begin reconfiguring tweak's key‐
119 board layout.
120
122 This section describes all the editing keys supported by tweak by
123 default. The default key bindings for tweak are basically Emacs-like.
124 Movement keys
126 The Emacs cursor movement keys should all work, and their counterparts
127 in ordinary function keys ought to work too:
128 · ^P and ^N go to the previous and next lines; Up and Down should
130 do the same.
131 · ^B and ^F go back and forward one character; Left and Right
133 should do the same.
134 · M-v and ^V go up and down one screenful at a time; Page Up and
136 Page Down should do the same.
137 · ^A and ^E go to the beginning and end of the line; Home and End
139 should do the same.
140 Press M-< and M-> go to the beginning and end of the file.
142 Press ^X g to go to a particular byte position in the file; you will be
144 asked to type in the position you want. You can enter it in decimal, or
145 as a hex number with `0x' before it.
146 Editing keys
148 Press Return to move the cursor between the hex section of the screen
149 and the ASCII section.
150 When in the hex section, you can enter hexadecimal digits to alter
152 data; when in the ASCII section, you can directly type ASCII text.
153 In ASCII mode, you can also press ^Q to literally quote the next input
155 character; for example, if you want to insert a Control-V, you can
156 press ^Q^V and tweak will automatically insert the byte value 0x16.
157 Press ^X^I, or the Insert key if you have one, to toggle between over‐
159 write mode and insert mode. In insert mode, typing hex or ASCII input
160 will insert new bytes containing the values you provide. Also, you can
161 then press Backspace to delete the byte to the left of the cursor, or
162 ^D or Delete to delete the byte under the cursor.
163 Cut and paste
165 Press ^@ (this character may be generated by the key combination Con‐
166 trol-@, or Control-2, or Control-Space) to mark the end of a selection
167 region. After you do this, the bytes between that mark and the cursor
168 will be highlighted. Press ^@ again to abandon the selection.
169 Press M-w while a selection is active to copy the selected region into
171 tweak's cut buffer.
172 In insert mode, you also have the option of pressing ^W to cut the
174 selected region completely out of the file and place it in the cut buf‐
175 fer.
176 Finally, press ^Y to paste the cut buffer contents back into the file
178 (this will overwrite or insert depending on the current mode).
179 Searching
181 Press ^S to search for a byte sequence. You will be asked to enter some
182 text to search for on the bottom line of the screen. You can type this
183 text in ASCII, or as a sequence of hex byte values prefixed with back‐
184 slashes (\). For example, if you wanted to search for the byte value 5
185 followed by the word `hello', you might enter \05hello. If you want to
186 specify a literal backslash character, you can either enter it in hex
187 (as \5C), or simply double it on input (\\).
188 Press ^R to search backwards instead of forwards from the current cur‐
190 sor position.
191 Since tweak deals in pure binary data, searches are always case-sensi‐
193 tive.
194 Controlling the display
196 If you press ^X w, you will be asked to enter a new display width. This
197 has the same effect as passing the -w option on the command line. Simi‐
198 larly, pressing ^X o allows you to enter a new display offset, equiva‐
199 lent to the -o option.
200 By default, the current file position and file size are displayed on
202 tweak's status line in hex. If you prefer them in decimal, you can
203 press ^X x or ^X h to toggle them between hex and decimal.
204 Miscellaneous
206 Press ^L to redraw the screen and recentre the cursor. Press ^Z to sus‐
207 pend tweak and return temporarily to the shell.
208 Press ^X^S to save the file you are editing.
210 Press ^X^C to exit tweak. (If you do this with changes unsaved, you
212 will be asked whether you want to save them.)
213
215 tweak's keyboard bindings are configurable. It will attempt to read a
216 file from your home directory called .tweakrc, and if it finds one it
217 will use the keyboard bindings described in it. If it does not find
218 one, it will use its internal default bindings.
219 Most of the directives in .tweakrc are of the form `bind command-name
221 key'. For example, `bind exit ^X^C'. Additionally, there are two other
222 directives, width and offset, which give the default display parameters
223 if no -w and -o options are specified.
224 The easiest way to learn about the .tweakrc file is to begin by having
226 tweak output its internal default one:
227 tweak -D > $HOME/.tweakrc
229 Then you can read the default file, learn the tweak internal command
231 names, and edit the file to do what you want.
232
234 This man page probably ought to contain an explicit list of internal
235 command names, rather than simply referring you to the default
236 .tweakrc.
237Simon Tatham 2004‐11‐05 tweak(1)